C PROGRAMMING PART B

SECTION - B
COMPETENCY OBJECTIVES
The objective of this Section is to provide the advanced features for programming with C language. It includes
complete explanations of these features. At the end of the course, a student should be able to :-
v Understand and implement Arrays.
v Appreciate the use of functions.
v Use the standard library string functions.
v Develop dynamic data structures in C.
v Understand structures and unions in C.
v Apply graphics features in C language.
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C LANGUAGE
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What are Arrays
Let us suppose we wish to arrange the percentage marks obtained by 100 students in ascending
order. In such a case there are two options to store these marks in memory:
(a) Construct 100 variables to store percentage marks obtained by 100 different students
i.e “each variable containing one students marks.
(b) Construct one variable (called array or subscripted variable) capable of storing or holding
all the hundred values.
Clearly, the second alternative is better because it would be much easier to handle one array
variable than handling 100 different variables
Now we can give a formal definition of array . An array is a collective name given to a group
of similar quantities. These similar quantities could be percentage marks of 100 students, or
salaries of 300 employee or ages of 50 employees. Thus an array is a collection of similar
elements. These similar elements could be all ints, or all floats or all chars etc. Usually, the
array of characters is called a ‘string’, where as an array of ints or floats is called simply an
array. All elements of any given array must be of the same type i.e we can’t have an array of
10 numbers, of which 5 are ints and 5 are floats.
ARRAY DECLARATION
To begin with, like other variables an array needs to be declared so that the compiler will
know what kind of an array and how. large an array we want.
for e.g. int marks [30];
Here int specifies the type of variable, marks specifies the name of the variable. The number
30 tells how many elements of the type int will be in our array. This number is often called the
‘dimension’ of the array. The bracket [ ] tells the compiler that we are dealing with an array.
CHAPTER - 6
ARRAYS
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C LANGUAGE
ACCESSING ELEMENTS OF AN ARRAY
To access an individual element in the array we have to subscript it, that is we have to put the
number in the brackets following the array name. All the array elements are numbered starting
with 0. Thus, marks [2] is not the second element of array but it is actually the third
element. Thus marks [i] refers to (i + 1) th element of the array.
Let us take an example of a program using array
main ( )
{ float avg, sum=0;
int i;
int marks [30]; /* array declaration*/
for ( i =0; i < = 29; i ++)
{
printf (“\n Enter marks “);
scanf (“%d”, &marks [i]);
}
for ( i = 0; i <= 29; i ++)
sum = sum + marks [i];
avg = sum /30;
printf (“\n Average marks = % f”, avg);
}
ENTERING DATA IN TO THE ARRAY
The section of code which places data in to an array is
for (i=0; i<= 29; i++)
{
printf (“\n Enter marks”)
scanf (“%d”, &marks [i]);
}
The above section will read about 30 elements numbered from 0 to 29 in to the marks array.
This will take input from the user repeatedly 30 times.
READING DATA FROM ARRAY
for ( i=0; i <= 29; i++);
sum = sum + marks [i];
avg = sum / 30;
printf (“\n Average marks = % f”, avg );
The rest of the program reads the data back out of the array and uses it to calculate the
average. The for loop is much the same, but now the body of loop causes each student’s
marks to be added to a running total stored in a variable called sum. When all the marks have
been added up, the result is divided by 30, the numbers of students to get the average.
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C LANGUAGE
Let us summarize the facts about array
(a) An array is a collection of similar elements.
(b) The first element in the array is numbered 0, the last element is 1 less than the
size of the array.
(c) An array is also known as subscripted variable .
(d) Before using an array its type and dimension must be declared.
(e) However big an array is, its elements are always stored in contiguous memory
locations.
ARRAY INITIALISATION
To initialise an array while declaring it. Following are a few examples which demonstrate this
int num [6] = {2, 4, 12, 5, 45, 5};
int n [ ] = {2, 4, 12, 5, 45, 5};
float press [ ] = { 12.3, 34.2, -23.4, - 11.3}
The following points should be noted
(a) Till the array elements are not given any specific values, they are suppose to
contain garbage values.
(b) If the array is initialized where it is declared mentioning the dimension of the
array is optional as in the 2nd example above.
MULTIDIMENSIONAL ARRAYS
In C one can have arrays of any dimensions. To understand the concept of multidimensional
arrays let us consider the following 4 x 5 matrix
0 10 4 3 -10 12
1 2 3 0 61 8
2 0 16 12 8 0
3 12 9 18 45 -5
Column numbers (j)
Row number (i)
Let us assume the name of matrix is x
To access a particular element from the array we have to use two subscripts on for row
number and other for column number the notation is of the form
X [i] [j] where i stands for row subscripts and j stands for column subscripts.
Below given are some typical two-dimensional array definitions
float table [50] [50];
char line [24] [40];
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C LANGUAGE
The first example defines tables as a floating point array having 50 rows and 50 columns. The
number of elements will be 2500 (50 X50).
The second declaration example establishes an array line of type character with 24 rows and
40 columns. The number of elements will be (24 X 40) 1920 consider the following two dimensional
array definition int values [3] [4] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10. 11, 12, };
Thus the array values can be shown pictorially as
0 1 2 3
0 1 2 3 4
1 5 6 7 8
2 9 10 11 12
Column number
Row number
Values [0] [0] = 1 Values [0] [1] = 2 Values [0] [2] = 3 Values [0] [3] = 4
Values [1] [0] = 5 Values [1] [1] = 6 Values [1] [2] = 7 Values [1] [3] = 8
Values [2] [0] = 9 Values [2] [1] = 10 Values [2] [2] = 11 Values [2] [3] = 12
Here the first subscript stands for the row number and second one for column number. First
subscript ranges from 0 to 2 and there are altogether 3 rows second one ranges from 0 to 3
and there are altogether 4 columns.
Alternatively the above definition can be defined and initialised as
int values [3] [4] = {
{ 1, 2, 3, 4}
{ 5, 6, 7, 8}
{9, 10, 11, 12}
};
Here the values in first pair of braces are initialised to elements of first row, the values of
second pair of inner braces are assigned to second row and so on. Note that outer pair of
curly braces is required.
If there are two few values within a pair of braces the remaining elements will be assigned as
zeros.
Here is a sample program that stores roll numbers and marks obtained by a student side by
side in matrix
main ( )
{
int stud [4] [2];
int i, j;
for (i =0; i < =3; i ++)
{
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printf (“\n Enter roll no. and marks”);
scanf (“%d%d”, &stud [i] [0], &stud [i] [1] );
}
for (i = 0; i < = 3; i ++)
printf (“\n %d %d”, stud [i] [0], stud [i] [1]);
}
The above example illustrates how a two dimensional array can be read and how the values
stored in the array can be displayed on screen.
ASSIMILATION EXERCISE
Q.1 Describe the array defined in each of the following statements
(a) char name [30] (d) # define A 66
(b) float c [6]; # define B 132
(c) int params [5] [5] (e) double account [50] [20] [80]
Q.2 How can a list of strings be stored within a two-dimensional array ? How can the
individual strings be processed? What library functions are available to simplify string
processing?
Q.3 Write a C program that will produce to table of value of equation
y = 2 e- 0.1t sin 0.5t
Where t varies between 0 and 60. Allow the size of the t - increment to be entered as an
input parameter.
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A computer program cannot handle all the tasks by it self. Instead its requests other program
like entities - called ‘functions in C - to get its tasks done. A function is a self contained block
of statements that perform a coherent task of some kind.
e.g
#include <stdio.h>
message();
{
message ( );
printf (“\n Hello “);
}
main ( )
{
message ( )
printf (“\n I am in main “);
}
output of the program will be
Hello
I am in main
Here main ( ) is the calling function and message is the called function. When the function
message ( ) is called the activity of main ( ) is temporarily suspended while the message ( )
function wakes up and goes to work. When the message ( ) function runs out of statements
to execute, the control returns to main ( ), which comes to life again and begins executing its
code at the exact point where it left off.
The General form of a function is
function (arg1, arg2, arg3)
type arg1, arg2, arg3
{
statement 1;
statement2;
statement3;
statement4;
}
CHAPTER - 7
FUNCTIONS
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C LANGUAGE
There are basically two types of functions
(i) Library functions e.g printf ( ), scanf ( ) etc
(ii) user defined function e.g the function message( ) mentioned above.
The following point must be noted about functions
(i) C program is a collection of one or more functions
(ii) A function gets called when the function name is followed by a semicolon for e.g.
main ( )
{
message ( );
}
(iii) A function is defined when function name is followed by a pair of braces in which one
or more statements may be present for e.g.
message ( )
{
statement 1;
statement2;
statement 3;
}
(iv) Any function can be called from any other function even main ( ) can be called from
other functions. for e.g.
main ( )
{
message ( );
}
message ( )
{
printf (“ \n Hello”);
main ( );
}
(v) A function can be called any number of times for eg.
main ()
{
message ( );
message ( );
}
message ( )
{
printf (“\n Hello”);
}
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C LANGUAGE
(vi) The order in which the functions are defined in a program and the order in which they
get called need not necessarily be same for e.g.
main ( );
{
message1 ( );
message2 ( );
}
message2 ( )
{
printf (“\n I am learning C”);
}
message1 ( )
{
printf ( “\n Hello “);
}
(vii) A function can call itself such a process as called ‘recursion’.
(viii) A function can be called from other function, but a function cannot be defined in another
function. Thus the following program code would be wrong, since argentina is
being defined inside another function main ( ).
main ( )
{
printf (“\n I am in main”);
argentina ( )
{
printf {“\n I am in argentina”);
}
}
(ix) Any C program contains at least one function
(x) If a program contains only one function, it must be main ( )
(xi) In a C program if there are more than one functional present then one of these functional
must be main ( ) because program execution always begins with main ( )
(xii) There is no limit on the number of functions that might be present in a C program.
(xiii) Each function in a program is called in the sequence specified by the function calls in
main ( )
(xiv) After each function has done its thing, control returns to the main ( ), when main ( ) runs
out of function calls, the program ends.
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C LANGUAGE
WHY USE FUNCTIONS
Two reasons :
(i) Writing functions avoids rewriting the same code over and over. Suppose that there is
a section of code in a program that calculates area of a triangle. If, later in the program
we want to calculate the area of a different triangle we wont like to write the same
instructions all over again. Instead we would prefer to jump to a ‘section of code’ that
calculates area and then jump back to the place from where you left off. This section of
code is nothing but a function.
(ii) Using functions it becomes easier to write programs and keep track of what they are
doing. If the operation of a program can be divided in to separate activities, and each
activity placed in a different function, then each could be written and checked more or
less independently. Separating the code in to modular functions also makes the program
easier to design and understand.
(a) Functions declaration and prototypes
Any function by default returns an int value. If we desire that a function should return a value
other than an int, then it is necessary to explicitly mention so in the calling functions as well as
in the called function. e.g
main ( )
{
float a,b,
printf (“\n Enter any number”);
scanf (“\% f”, &a );
b = square (a);
printf (“\n square of % f is % f”, a,b);
}
square (Float x)
{
float y;
y = x * x;
return (y);
}
the sample run of this program is
Enter any number 2.5
square of 2.5 is 6.000000
Here 6 is not a square of 2.5 this happened because any C function, by default, always
returns an integer value. The following program segment illustrates how to make square ( )
capable of returning a float value.
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C LANGUAGE
main ( )
{
float square ( );
float a, b;
printf (“\n Enter any number “);
scanf (“%f” &a);
b = square (a);
printf (“\n square of % f is % f, “ a, b);
}
float square (float x)
{
float y;
y= x *x;
return ( y);
}
sample run
Enter any number 2.5
square of 2.5 is 6.2500000
CALL BY VALUE
In the preceding examples we have seen that whenever we called a function we have always
passed the values of variables to the called function. Such function calls are called ‘calls by
value’ by this what it meant is that on calling a function we are passing values of variables to
it.
The example of call by value are shown below ;
sum = calsum (a, b, c);
f = factr (a);
In this method the value of each of the actual arguments in the calling function is copied into
corresponding formal arguments of the called function. With this method the changes made
to the formal arguments in the called function have no effect on the values of actual argument
in the calling function. the following program illustrates this
main ( )
{
int a = 10, b=20;
swapy (a,b);
printf (“\na = % d b = % d”, a,b);
}
swapy (int x, int y)
{
int t;
t = x;
x = y;
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y = t;
printf ( “\n x = % d y = % d” , x, y);
}
The output of the above program would be;
x = 20 y = 10
a =10 b =20
CALL BY REFERENCE
In the second method the addresses of actual arguments in the calling function are copied in
to formal arguments of the called function. This means that using these addresses we would
have an access to the actual arguments and hence we would be able to manipulate them the
following program illustrates this.
main ( )
{
int a = 10, b =20,
swapr (&a, &b);
printf (“\n a = %d b= %d”, a, b);
}
swapr (int *x, int * y)
{
int t;
t = *x
*x = *y;
*y = t;
}
The output of the above program would be
a = 20 b =10
ASSIMILATION EXERCISE
Q.1 Each of the following is the first live of a function definition explain the meaning of each
(a) float f (float a, float b) (c) Void f (int a)
(b) long f ( long a ) (d) char f (void)
Q.2 Write a function that will calculate and display the real roots of the quadratic equation:
ax 2 + bx + c = 0 using the quadratic formula
x =
2a
- b ± b2 - 4ac
Assume that a, b and c are floating - point arguments where values are given and that
x1 and x2 are floating point variables. Also assume that b2 > 4 * a * c , so that the
calculated roots will always be real.
Q.3 Write a function that will allow a floating - point number to be raised to an integer
power. In other words, we wish to evaluate the formula
y = Xn
where y and x are floating - point variables and n is an integer variable.
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For string handling C provides a standard set of library functions. Though there exists many
such functions four of them will be discussed here.
The strcmp( ) Function
This function is used to check whether two strings are same or not. If both the strings are
same it return a 0 or else it returns the numeric difference between the ASCII values of
nonmatching characters e.q. the following program
# include <stdio.h>
main( )
{
char string1 [ ] = “orange”;
char string2 [ ] = “banana”;
printf(“%d\n”, strcmp(string1, string2));
printf(“%d\n”, strcmp(string2, “banana”);
printf(“%d”, strcmp(string1, “Orange”));
getch( );
}
output
13
0
32
In the first printf statement we use the strcmp( ) function with string1 and string2 as it arguments.
As both are not equal (same) the function strcmp( ) returned 13, which is the numeric
difference between “orange” and “banana” ie, between string2 and b.
In the second printf statement the arguments to strcmp() are string2 and “banana”. As string2
represents “banana”, it will obviously return a 0.
In the third printf statement strcmp( ) has its arguments “orange” and “Orange” because
string1 represents “Orange”. Again a non-zero value is returned as “orange” and “Orange”
are not equal.
CHAPTER - 8
STANDARD LIBRARY STRING FUNCTIONS
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C LANGUAGE
strcpy( ) Function
The function copies one string to another for e.g. the following program
# include <stdio.h>
main( )
{
char source [ ] = “orange”;
char target [20];
strcpy(target, source);
clrscr( );
printf(“source: %s\n”, source);
printf(“target:%s”, target);
getch( );
}
output will be
source : orange
target : orange
strcat( )
This function concatenates the source string at the end of the target string for e.g, “Bombay”
and “Nagpur” on concatenation would result in to a string “Bombay Nagpur”. Here is an example
of strcat( ) at work.
main( )
{
char source [ ] = “Folks”;
char target [30] = “Hello”;
strcat(target, source);
printf(“\n source string = %s”, source);
printf(“\n target string = %s”, target);
}
And here is the output
source string = folks
target string = Hello folks
strlen( )
This function counts the number of characters present in a string. Its usage is illustrated in the
following program.
main( )
{
char arr[ ] = “Bamboozled”
int len1, len 2;
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len1 = strlen(arr);
len2 = strlen(“Hunpty Dumpty”);
printf(“\n string = %s length = %d”, arr, len1);
printf(“\n string = %s length = %d”, “Humpty Dumpty”, len2);
}
The output would be
string = Bamboozled length=10
string = Humpty Dumpty length = 13
while calculating the length of the string it does not count ‘\0’.
ASSIMILATION EXERCISE
Q.1 Write a function xstrstr ( ) that will return the position where one string is present within
another string. If the second string doesn’t occur in the first string xstrstr ( ) should
return a0.
For example in the string “ some where over the rainbow”, “over” is present at position”
Q.2 Write a program to encode the following strings such that it gets convert into an
unrecognisable from. Also write a decode function to get back the original string.
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POINTERS
THE & and * Operators
A pointer is a variable that represents the location of a data item, such as a variable or an
array element. Pointers are used frequently in C, as they have a number of useful applications.
For example, pointers can be used to pass information back and forth between a function
and its reference point. Pointers provide a way to return multiple data items from a function
via function arguments to be specified as arguments to a given function.
Pointers are also closely associated with arrays and therefore provide an alternate way to
access individual array elements.
Within the computer’s memory, every stored data item occupies one or more adjacent memory
cells. The number of memory cells required to store a data item depends on the type of data
item. For example, a single character will be stored in 1 byte of memory integer usually
requires two adjacent bytes, a floating point number may require four adjacent bytes.
Suppose V is a variable that represents some particular data item. The compiler will automatically
assign memory cells for this data item. The data item can be accessed if we know the
location of the first memory cell. The address of V’s memory location can be determined by
the expression &V, where & is a unary operator, called the address operator, that evaluates
the address of its operand.
Now let us assign the address of V to another variable, PV. Thus,
PV = & V
This new variable is called a pointer to V, since it “Points” to the location where V is stored in
memory. Remember, however, that PV represents V’s address, not its value. Thus, PV is
called pointer variable.
CHAPTER - 9
DYNAMIC DATA STRUCTURES IN C
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C LANGUAGE
address of V value of V
PV V
Relationship between PV and V (where PV = &V and V = *PV)
The data item represented by V can be accessed by the expression *PV where * is a unary
operator, that operates only on a pointer variable. Therefore, PV and V both represent the
same data item. Furthermore, if we write PV = &V and U = PV, then U and V will both
represent the same values i.e., the value of V will indirectly be assigned to U.
Example :
int quantity = 179 ;
The statement instructs the system to find a location for the integer quantity and puts the
value 179 in that location. Let us reassume that the system has chosen the address location
5000 for quantity.
Quantity
179
5000
Variable
Value
Address
Representation of a variable
Remember, since a pointer is a variable, its value is also stored in the memory in another
location.
The address of P can be assumed to be 5048.
Variable
Quantity
P
Value
179
5000
Address
5000
5048
Pointer as a variable
Declaring and initializing Pointers
Since pointer variables contain addresses that belong to a separate data type, they must be
declared as pointers before we use them. The declaration of a pointer variable takes the
following form:
data type * Pt _ name
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C LANGUAGE
This tells the compiler three things about the variable Pt_name.
1. The * tells that the variable Pt_name is a pointer variable.
2. Pt_name needs a memory location.
3. Pt_name ponts to a variable of type data type.
Example : int * P ;
Declares the variable P as a pointer variable that points to an integer data type.
float * y ;
declares y as a pointer to a floating point variable.
Once pointer variable has been declared, it can be made to point to a variable using an
assignment statement such as
P = & quantity ;
which causes P to point to quantity. P contains the address of quantity. This is known as
pointer initialization.
Pointer expressions
Like other variables, pointer variables can be used in expressions. For example, if P1 and P2
are properly declared and initialized pointers, then the following statements are valid.
1) Y = * P1 ;
2) Sum = Sum + * P1 ;
3) Z = S - * P2 / * P1 ;
4) * P2 = * P2 + 10 ;
Note that there is a blank space between / and * in the item 3 above.
If P1 and P2 are pointers then the expressions such as,
P1 + 4 , P2 - 2 , P1 - P2 , P1 ++ , — P2 are allowed
also,
Sum =Sum + *P2 ;
P1 ++ ;
- -P2 ;
P1 > P2
P1 = = P2
P1 ! = P2
are all allowed expressions.
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C LANGUAGE
The expressions such as,
P1 / P2 or P1 * P2 or P1/3
are not allowed.
Pointer assignments
After declaring a pointer, pointer is assigned a value, so that it can point to a particular variable.
eg. int * P ;
int i ;
P = & i ;
This is called assignment expression in which pointer variable P is holding the address of i.
Pointer arithmetic
Two pointer values can be added, multiplied, divided or subtracted together.
eg. if int i ;
int j ;
int * P , * q ;
i = 5 , j = 10 ;
Now, various pointer arithmetic can be performed
eg. * j = * i + * j ;
The value of variable j is changed from 10 to 15.
* j = * j - * i ;
The value of variable j is changed from 10 to 5.
* i = * i ** j ;
The value of i is changed from 5 to 50 ;
Consider another example,
if there is array and a pointer is pointing to it
int i [10] ;
int * P ;
P = i ;
Now, arithmetic operations like
P = P + 4 ;
Will move the pointer P from the starting address of the array to the fourth subscript of array.
Similarly, if P1 and P2 are both pointers to the same array, then P2 - P1 gives the number of
elements between P1 and P2.
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arithmetic operations like
P1/P2 or P1 x P2 or P/3 are not allowed.
Pointer Comparison
In addition to arithmetic operations, pointers can also be compared using the relational operators.
The expressions such as
P1 > P2 , P1 = = P2 , P1 ! = P2 are allowed.
However, any comparison of pointers that refer to separate and unrelated variables make no
sense. Comparisons can be used meaningfully in handling arrays and strings.
The dynamic allocation functions - malloc( ) and calloc( )
Most often we face situations in programming where the data is dynamic in nature. That is,
the number of data items keep changing during execution of the program. For example,
consider a program for processing the list of customers of a company. The list grows when
names are added and shrinks when names are deleted. When list grows we need to allocate
more memory space to the list to accommodate additional data items. Such situations can be
handled more easily and effectively by using what is called dynamic data structures.
DYNAMIC MEMORY ALLOCATION
C language requires that the number of elements in an array should be specified at compile
time. Our initial judgement of size, if it is wrong, may cause failure of the program or wastage
of memory space.
Many languages permit a programmer to specify an array’s size at run time. Such languages
take the ability to calculate and assign, during execution, the memory space required by the
variables in a program. The process of allocating memory at run time is known as dynamic
memory allocation. The library functions used for allocating memory are :
Function Task
malloc ( ) Allocates requested size of bytes and returns a pointer to the
first byte of the allocated space.
calloc ( ) Allocates space for an array of element, initializes them to
zero and then returns a pointer to the memory.
Memory Allocation Process
Let us first look at the memory allocation process associated with a C program. Fig. below
shows the conceptual view of storage of a C program in memory.
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C LANGUAGE
Local Variable
Free Memory
Global
Variables
C Program
Instructions
Scale
Heap
The program instructions and global and static variables are stored in a region known as
permanent storage area and the local variables are stored in another area called stack. The
memory space that is located between these two regions is available for dynamic allocation
during execution of the program. The free memory region is called the heap. The size of the
heap keeps changing when program is executed due to creation and death of variables that
are local to functions and blocks. Therefore, it is possible to encounter memory “overflow”
during dynamic allocation process. In such situations, the memory allocations functions mentioned
above returns a NULL pointer.
ALLOCATING A BLOCK OF MEMORY
A block of memory may be allocated using the function malloc. The malloc function reserves
a block of memory of specified size and returns a pointer of type void. This means that we can
assign it to any type of pointer. It takes the following form;
ptr = ( Cast type * ) malloc ( byte size ) ;
ptr is a pointer of type cast type. The malloc returns a pointer (of cast type) to an area of
memory with size byte - size.
Example :
X = ( int * ) malloc ( 100 *sizeof ( int )) ;
On successful execution of this statement, a memory space equivalent to “100 times the size
of an int” bytes is reserved and the address of the first byte of the memory allocated is assigned
to the pointer X of type int.
Similarly, the statement
Cptr = ( char * ) malloc (10) ;
allocates 10 bytes of space for the pointer Cptr of type char
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C LANGUAGE
Cptr
2000
1000
0 1 2 . . . . . . 9
Remember, the malloc allocates a block of adjacent bytes. The allocation can fail if the space
in the heap is not sufficient to satisfy the request. If it foils, it returns a NULL. We should
therefore check whether the allocation is successful before using the memory pointer.
Example :
Write a program that uses a table of integers whose size will be specified interactively at run
time.
Program -
# include <stdio. h>
# include <stdlib.h>
# define NULL O
main ( )
{
int * P, * table ;
int size ;
printf ( “\n What is the sizeof table ? “ ) ;
scanf ( “ % d”, &size ) ;
printf ( “\n” ) ;
if (( table = (int * ) malloc (size * sizeof (int)) = = NULL )
{
printf (“No space available \ n”) ;
exit ( 1) ;
}
printf (“\n address of the first byte is % u\n”, table );
printf(“\n Input table values”);
for ( P = table; P < table + size; P++ )
scanf (“%d”, *P );
for ( P = table + size - 1; P > = table; P- - )
printf (“%d is stored at address %u\n”, *P, P );
}
Allocating Multiple Blocks of Memory
calloc is another memory allocation function that is normally used for requesting memory
space at runtime for storing derived data types such as arrays and structures. While malloc
allocates a single block of storage space, calloc allocates multiple blocks of storage, each of
the same size, and then allocates all bytes to O. The general form of calloc is :
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C LANGUAGE
ptr = (Cast type * ) calloc ( n, elem_size );
The above statement allocates contiguous space for n blocks, each of size elem-size bytes.
All bytes are initialized to zero and a pointer to the first byte of the allocated region is returned.
If there is not enough space, a NULL pointer is returned.
The following program allocates space for a structure variable.
#include < stdio.h>
#include < stdlib.h>
struct student
{
char name (25);
float age;
long int num;
} ;
typedef struct student record ;
record * ptr ;
int class_size = 30 ;
ptr = ( record * ) calloc ( class_size, sizeof ( record )) ;
- - - -
- - - -
record is of type struct student having three number :
name, age and num. The calloc allocates memory to hold data for 30 such records. We
should check if the requested memory has been allocated successfully before using the ptr.
This may be done as follows:
if ( ptr == NULL )
{
printf ( “Available memory not sufficient”) ;
exit ( 1 ) ; }
POINTERS VS. ARRAY
When an array is declared, the compiler allocates a base address and sufficient amount of
storage to contain all the elements of the array in contiguous memory locations. The base
address is the location of the first element (index 0) of the array. The compiler also defines the
array name as a constant pointer to the first element suppose we declare an array X as
follows :
static int X [ 6 ] = { 1, 2, 3, 4, 5, 6 } ;
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C LANGUAGE
Suppose the base address of X is 1000 and assuming that each integer requires two bytes,
the five elements will be stored as follows :
ELEMENTS x [0] x[1] x[2] x[3] x[4] x[5]
VALUE 1 2 3 4 5 6
Address 1000 1002 1004 1006 1008 1010
BASE ADDRESS
The name X is defined as a constant pointer pointing to the first clement,
x[0] and therefore the value of X is 1000, the location whose X[0] is stored. That is ;
X = & x[0] = 1000
If we declare P as an integer pointer, then we can make the pointer P to point to the array X
by the following assignment :
P = X ;
This is equivalent to P = & X[0] ;
Now we can access every value of x using P++ to move from one element to another. The
relationship between P and X is shown below :
P = & x[0] ( = 1000)
P+1 = & x[1] ( = 1002)
P+2 = & x[2] ( = 1004)
P+3 = & x[3] ( = 1006)
P+4 = & x[4] ( = 1008)
P+5 = & x[5] ( = 1010)
The address of an element is calculated using its index and the scale factor of the data type.
For instance,
address of X[3] = base address + (3 x Scale factor of int)
= 1000 + (3 x 2) = 1006
When handling array, instead of using array indexing, we can use pointers to access array
elements. Note that *(x+3) gives the value of X[3]. The pointer accessing method is more
faster than array indexing.
POINTERS AND FUNCTIONS
When an array is passed to a function as an argument, only the address of the first element of
the array is passed, but not the actual values of the array elements. The function uses this
address for manipulating the array elements. Similarly, we can pass the address of a variable
as an argument to a function in the normal fashion.
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C LANGUAGE
When we pass addresses to a function, the parameters receiving the addresses should be
pointers. The process of calling function using pointers to pass the address of variable is
known as call by reference. The function which is called by reference can change the value of
the variable used in the call.
eg.
main ( )
{
int X ;
X = 40 ;
change ( & X ) ;
printf ( “ %d”, X ) ;
{
change ( int * P )
{
* P = * P + 10 ;
}
When the function change is called, the address of the variable X, not its value, is passed into
the function change ( ). Inside change ( ), the variable P is declared as a pointer and therefore
P is the address of the variable X. The statement,
* P = * P + 10 ;
means add 10 to the value stored at address P. Since P represents the address of X, the
value of X is changed from 50. Therefore, the output of the program will be 50 not 40.
Thus, call by reference provides a mechanism by which the function can change the stored
values in the calling function.
POINTERS TO FUNCTIONS
A function like a variable, has an address location in the memory. It is therefore, possible to
declare a pointer to a function, which can then be used as an argument in another function. A
pointer to a function is declared as follows:
type ( * fp) ( ) ;
This tells the compiler that fp is a pointer to a function which returns type value.
We can make a function pointer to point to a specific function by simply assigning the name of
the function to the pointer.
For example,
double (*P1)( ), mul ( ) ;
P1 = mul ;
declare P1 as a pointer to a function and mul as a function and then make P1 to point to the
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C LANGUAGE
function mul. To call the function mul, we may now use the pointer P1 with the list of parameters.
That is,
(*P1) (x,y)
is equivalent to mul ( x,y )
FUNCTIONS RETURNING POINTERS
The way functions return an int, a float, a double or any other data type, it can even return a
pointer. However, to make a function return a pointer it has to be explicitly mentioned in the
calling function as well as in the function declaration. The following program illustrates this
main ( )
{
int * P ;
int * fun ( ) ;
P = fun ;
printf ( “\n % Id”, P ) ;
}
int * fun ( )
{
int i = 20;
return (& i) ;
}
In this program, function fun( ) is declared as pointer returning function can return the address
of integer type value and in the body of the function fun ( ) we are returning the address of
integer type variable i into P which is also integer type pointer.
POINTERS AND VARIABLE NUMBER OF ARGUMENTS
We use printf ( ) so often without realizing how it works correctly irrespective of how many
arguments we pass to it. How do we write such routines which can take variable number of
arguments? There are three macros available in the file “stdarg.h” called va_start, va_arg and
va_list which allow us to handle this situation. These macros provide a method for accessing
the arguments of the function when a function takes a fixed number of arguments followed by
a variable number of arguments. The fixed number of arguments are accessed in the normal
way, whereas the optional arguments are accessed using the macros va_start and va_arg.
Out of these macros va_start is used to initialise a pointer to the beginning of the list of
optional arguments. On the other hand the macro va_arg is used to initialise a pointer to the
beginning of the list of optional arguments. On the other hand the macro va_arg is used to
advance the pointer to the next argument.
eg. # include < stdarg. h >
# include < stdio. h >
main ( )
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C LANGUAGE
{
int max ;
max = findmax ( 5, 23, 15, 1, 92, 50 ) ;
printf (“\n max = % d”, max ) ;
max = findmax (3, 100, 300, 29 ) ;
printf (“\n max = %d”, max ) ;
}
findmax (int tot_num)
{
int max, count, num ;
va_list ptr ;
va_start ( ptr, tot_num ) ;
max = va_arg (ptr, int ) ;
for ( count = 1 ; count < tot_num ; count + + )
{
num = va_arg (ptr, int ) ;
if ( num > max )
max = num ;
}
return ( max ) ;
}
Here we are making two calls to findmax( ) first time to find maximum out of 5 values and
second time to find maximum out of 3 values. Note that for each call the first argument is the
count of arguments that are being passed after the first argument. The value of the first
argument passed to findmax ( ) is collected in the variable tot_num findmax( ) begins with a
declaration of pointer ptr of the type va_list. Observe the next statement carefully
va_start ( ptr, tot_num ) ;
This statements sets up ptr such that it points to the first variable argument in the list. If we are
considering the first call to findmax ( ) ptr would now point to 23. The next statement max =
va_arg ( ptr, int ) would assign the integer being pointed to by ptr to max. Thus 23 would be
assigned to max, and ptr will point to the next argument i.e. 15.
POINTERS TO POINTERS
The concept of pointers can be further extended. Pointer we know is a variable which
contains address of another variable. Now this variable itself could be another pointer.
These we now have a pointer which contains another pointer’s address. The following
example should make this point clear.
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C LANGUAGE
main ()
{
int i = 3 ;
int * j ;
int * * k ;
j = & i ;
k = & j ;
printf (“\n address of i = % \d”, & i );
printf (“\n address of i = % \d”, j );
printf (“\n address of i = % \d”, * k );
printf (“\n address of j = % \d”, & j );
printf (“\n address of j = % \d”, k );
printf (“\n address of k = % \d”, & k );
printf (“\n address of k = % \d”, &k );
}
In this program i is an integer type value, j is a pointer to this variable and k is another pointer
type variable pointing to j.
i j k
3 6485 3276
6485 3276 7234
All the addresses are assumed addresses K is pointing to the variable j. These K is a pointer
to pointer. In principle, there could be a pointer to a pointer’s pointer, of a pointer to a pointer
to a pointer’s pointer. There is no limit on how far can we go on extending this definition.
ARRAY OF POINTERS
The way there can be an array of ints or an array of floats, similarly there can be an array of
pointers. Since a pointer variable always contain an address, an array of pointers would be
nothing but collection of addresses. The addresses present in the array of pointers can be
addresses of isolated variables or addresses of array elements or any other addresses. All
rules that apply to an ordinary array apply to the array of pointers as well.
eg. main ( )
{
int * arra [ 4 ];
int i = 31, j = 5, k = 19, L = 71, m;
arra [0] = & i ;
arra [1] = & j ;
arra [2] = & k ;
arra [3] = & l ;
i j
3 6485
6485 3276
k
3276
7234
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C LANGUAGE
for (m=0; m<=3 ; m+ +)
printf (“\n% d”, * (arr[m])) ;
}
The output will be -
31
5
19
71
i j k l
31 5 19 71
4008 5116 6010 7118
arr[0] arr[1] arr[2] arr[3]
4008 5116 6010 7118
7602 7604 7606 7608
ASSIMILATION EXERCISE
Q.1 What is the purpose of an automatic variable? What is its scope?
Q.2 A C program contains the following declaration:
static char * color[6] { “red”, “green”, “blue”, “white”, “black”, “yellow”}
(a) What is the meaning of color?
(b) What is the meaning of (color + 2)?
(c) What is the value of * color ?
(d) What is the value of * (color +2)?
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C LANGUAGE
Introduction
A structure is a convenient tool for handling a group of logically related data items. structure
help to organize complex data in a more meaningful way. It is powerful concept that we may
after need to use in our program Design. A structure is combination of different data types
using the & operator, the beginning address of structure can be determined. This is variable is
of type structure, then & variable represent the starting address of that variable.
structure Definition
A structure definition creates a format that may be used to declare structure variables consider
the following example.
struct book_bank
{
char title [20];
char author [15];
int pages;
float price;
};
Here keyword struct hold the details of four fields these fields are title, author, pages, and
price, these fields are called structure elements. Each element may belong to different types
of data. Here book_bank is the name of the structure and is called the structure tag.
It simply describes as shown below.
struct book-bank
Title array of 20 characters
Author array of 15 characters
Pages integer
Price float
]
CHAPTER - 10
STRUCTURES AND UNION
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C LANGUAGE
The general format of a structure definition is as follows
struct teg_name
{
data_type member 1;
data_type member 2;
- - - - - -
- - - - - -
- - - - - -
}
Array of structures
Each element of the array itself is a structure. See the example shown below. Here we want to
store data of 5 persons for this purpose, we would be required to use 5 different structure
variables, from sample1 to sample 5. To have 5 separate variable will be inconvenient.
# include <stdio.h>
main( )
{
struct person
{
char name [25];
char age;
};
struct person sample[5];
int index;
char into[8];
for( index = 0; index <5; index ++)
{
print(“Enter name;”);
gets(sample [index]. name);
printf(“%age;”);
gets(info);
sample [index]. age = atoi (info);
}
for (index = 0; index <5; index++)
{
printf(“name = %5\n”, sample [index]. name);
printf(“Age = %d \n”, sample [index]. age);
getch( );
}
}
The structure type person is having 2 elements:
Name is an array of 25 characters and character type variable age
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C LANGUAGE
Using the statement:
struct person sample[5]; we are declaring a 5 element array of structures. Here, each element
of sample is a separate structure of type person.
We, then defined 2 variable indexes and an array of 8 characters’ info.
Here, the first loop executes 5 times, with the value of index varying from 0 to 4. The first printf
statement displays. Enter name gets( ) function waits for the input string. For the first time this
name you enter will go to sample[0]. name. The second printf display age the number you
type is will be 5 stored as character type, because the member age is declared as character
type. The function atoi( ) converts this into an integer. atoi stands for alpha to integer. This
will be stored in sample[0] age. The second for loop in responsible for printing the information
stored in the array of structures.
structures within structures:-
structure with in a structure means nesting of structures. Let us consider the following structure
defined to store information about the salary of employees.
struct salary
{
char name[20];
char department[10];
int basic_pay;
int dearness_allowance;
int city_allowance;
}
employee;
This structure defines name, department, basic pay and 3 kinds of allowance. we can group
all the items related to allowance together and declare them under a substructure as shown
below:
struct salary
{
char name [20];
char department[10];
struct
{
int dearness;
int hous_rent;
int city;
}
allowance;
}
employee;
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C LANGUAGE
The salary structure contains a member named allowance which itself is a structure with 3
members. The members contained in the inner, structure namely dearness, hous_rent, and
city can be referred to as :
employee allowance. dearness
employee. allowance. hous_rent
employee. allowance. city
An inner-most member in a nested structure can be accessed by chaining all the concerned.
structure variables (from outer-most to inner-most) with the member using dot operator. The
following being invalid.
employee. allowance (actual member is missing)
employee. hous_rent (inner structure variable is missing)
Passing a structure as a whole to a Function:
structures are passed to functions by way of their pointers. Thus, the changes made to the
structure members inside the function will be reflected even outside the function.
# include <stdio.h>
typedef struct
{
char *name;
int acc_no;
char acc_types;
float balance;
} account;
main( )
{
void change(account *pt);
static account person = {“chetan”, 4323, ‘R’, 12.45};
printf(“%s %d %c %2.f \n”, person. name,
person.acc_type, person. acc_type,
person. balance);
change(&person);
printf(“%s %d %c %2.f \n”, person.name, person.acc_type,
person.acc-type, person. balance);
getch( );
}
void change(account *pt)
{
pt - > name =” Rohit R”;
pt - > acc_no = 1111;
pt - > acc_type = ‘c’;
pt - > balance = 44.12;
}
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C LANGUAGE
output
chetan 4323 R 12.45
Rohit R 1111 c 44.12
UNIONS
Unions, like structure contain members, whose individual data types may vary. This is a is
major distinction between them in terms of storage .In structures each member has its own
storage location, where as all the members of a union use the same location.
Like structures, a union can be declared using the keyword union is follows:
union item
{
int m;
float x;
char c;
} code;
This declares a variable code of type union item. The union contains item members, each
with a different date type. However, we can use only one of them at a time. This is due to the
fact that only one location is allocated for a union variable, irrespective of its size
Storage 4 bytes
1000
c
m
x
1001 1002 1003
The compiler allocates a piece of storage that is large enough to hold the largest variable
type in the union. In the declaration above, the member x requires 4 bytes which is the largest
among the members. The above figure shown how all the three variables share the same
address, this assumes that a float variable requires 4 bytes of storage.
To access a union member, we can use the same syntax that we as for structure members,
that is,
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C LANGUAGE
code. m
code. x
code. c are all valid
When accessing member variables, we should make sure that we are accessing the member
whose value is currently in storage. For example
code. m = 565;
code. x = 783.65;
printf(“%d”, code. m); would produce erroneous output.
# include <stdio.h>
main( )
{
union
{
int one;
char two;
} val;
val. one = 300;
printf(“val. one = %d \n”, val. one);
printf(“val. two = %d \n”, val. two);
}
The format of union is similar to structure, with the only difference in the keyword used.
The above example, we have 2 members int one and char two we have then initialised the
member ‘one’ to 300. Here we have initialised only one member of the union. Using two
printf statements, then we are displaying the individual members of the union val as:
val. one = 300
val. two = 44
As we have not initialised the char variable two, the second printf statement will give a
random value of 44.
The general formats of a union thus, can be shown as.
union tag {
member 1;
member 2;
- - -
- - -
member m;
};
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C LANGUAGE
The general format for defining individual union variables:
Storage-class Union tag variable 1, variable 2,........., variable n;
Storage-class and tag are optional variable 1, variable 2 etc, are union variable of type tag.
Declaring union and defining variables can be done at the same time as shown below:
Stroage-calss union tag {
member 1;
member 2;
- - -
- - -
- - -
member m;
} variable 1, variable 2, - - - , variable n;
ASSIMILATION EXERCISE
Q.1 struct book_bank
{
char title[20];
char author[15];
int pages;
float price;
};
The above structure requires __________ bytes of memory.
Q.2 union book_bank
{
char title[20];
char author[15];
int pages;
float price;
};
The above union requires __________ bytes of memory.
Q.3 struct marks
{
int maths;
int physics;
int chemistry;
char name[30]
};
Sort the above structure for 10 students according to the total of marks .
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C LANGUAGE
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C LANGUAGE
CHAPTER - 11
DISK I/O FUNCTIONS
scanf( ), printf( ), getch ( ) etc which we have studied were console I/O functions. Let us now
turn our attention to disk I/O. Disk I/O operations are performed on entities called files. The
brief categorisation of Disk I/O functions is given below
DISK I/O FUNCTIONS
High Level
Text
Formatted Formatted
Low Level
Binary
Unformatted Unformatted
From above we can see that the file I/o functions are further categorised in to text and binary.
This classification arises out of the mode in which a file is opened for input or output. Which of
these two modes is used to open the file determines:
(a) How new lines (\n) are stored
(b) How end of file is indicated
(c) How numbers are stored in the file
Opening a file
We make the following declaration before opening a file
FILE * fp
Now let us understand the following statements,
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C LANGUAGE
FILE * fp;
fp = fopen (“PR1.C”,”r”);
fp is a pointer variable which contains address of the structure FILE which has been defined
in the header file “stdio.h”.
fopen( ) will open a file “PRI.C” in read mode. fopen( ) performs three important tasks when
you open the file in
“r” mode:
(i) Firstly it searches on the disk the file to be opened.
(ii) If the file is present, it loads the file from the disk in to memory. Of course if the file is
very big, then it loads the file part by part.
If the file is absent, fopen( ) returns a NULL. NULL is a macro defined in “stdio.h” which
indicates that you failed to open the file.
(iii) It sets up a character pointer (which is part of the FILE structure) which points to the
first character of the chunk of memory where the file has been loaded.
# include <stdio.h>
main( )
{
FILE *fp;
fp = fopen(“PRI.C”, “r”);
if (fp= = NULL)
{ puts (“ cannot open file”);
exit( );
}
}
Closing the file
The closing of the file is done by fclose( ) through the statement,
fclose ( fp );
File Opening Modes
The “r” mode mentioned above is one of the several modes in which we can open a file.
These are mentioned below:
(i) “r” Searches the file. If the file exists, loads it in to memory and sets up a pointer which
points to the first character in it. If the file doesn’t exist it returns NULL.
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C LANGUAGE
(ii) “w” Searches file if the file exists it contents are overwritten. If the file doesn’t exist, a
new file is created. Returns NULL, if unable to open file.
Operations possible - writing to the file.
(iii) “a” Searches file. If the file exists, loads it in to memory and sets up a pointer which
points to the first character in it. If the file doesn’t exist a new file is created. Returns
NULL, if unable to open file. Operations possible - Appending new contents at the
end of file.
(iv) “r+” Searches file. If it exists, loads it in to memory and sets up a pointer which points
to the first character in it. If file doesn’t exist it returns NULL.
Operations possible - reading existing contents, writing new contents, modifying
existing contents of the file.
(v) “w+” Searches file. If the file exists, it contents are destroyed. It the file doesn’t exist a
new file is created. Returns NULL if unable to open file. Operations possible - writing
new contents, reading them back and modifying existing contents of the file. “a+”
Searches if the file exists, loads it in to memory and sets up a pointer which points to
the first character in it. If the file doesn’t exist, a new file is created. Returns NULL, if
unable to open file. Operations possible - reading existing contents, appending new
contents to the end of file. Canot modify existing contents.
Reading from a File(Unformatted Character)
To read the file’s contents from memory there exists a function called fgetc( )
e.g ch = fgetc(fp);
Writing to a File(Unformatted Character)
There exists a fputc( ) function that writes to the file fputc(ch, ft);
here value of ch variable will be written to file whose file pointer is ft.
Closing the File
When we have finished reading or writing from the file, we need to close it. This is done using
the function fclose( ) through the statement.
fclose(fp); fp is file pointer here.
e.g Afile - copy program here is a program which copies the contents of one file in to
another
# include <stdio.h>
main( )
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C LANGUAGE
{
FILE *fs, *ft;
char ch;
fs = fopen(“pr1.c”, “r”);
if(fs = = NULL)
{
puts(“canot open source file”)’
exit( );
}
ft = fopen (“pr2.c”, “w”);
it (ft = =NULL)
{
puts(“canot open target file”);
fclose(fs);
exit( );
}
while (1)
{
ch = fgetc(fs);
if(ch = = EOF)
break;
else
fputc(ch,ft);
}
fclose(fs);
fclose(ft);
}
The fprintf and fscanf functions(Formatted I/o)
The general form of fprintf is
fprintf(fp, “control string”, list)
eg fprintf(f1, “%s %d %f”, name, age, 7.5);
Name is an array variable of type char and age is an int variable. The function fprintf will
cause the value name age and 7.5 to be written to the file pointed by variable f1.
The general format of fscanf is
fscanf(fp, “control string”, list);
This statement would cause the reading of the items in the list from the file specified by fp,
according to the specifications contained in the control string. eg.
fscanf(f2, “%s %d”, item, & quantity);
Like scanf fscanf also returns number of items that are successfully read. When the end of the
file is reached, it returns the value EOF.
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C LANGUAGE
fseek function
fseek function is used to move the file position to a desired location within the file. It takes the
following form:
fseek(file ptr, offset, position)
File ptr is a pointer to the file concerned, offset is a number variable of type long and position
is an integer number. The offset specifics the number of positions(bytes) to the moved from
the location specified by position.
The position can take one of the following three values
Values Meaning
0 Beginning of file
1 Current position
2 End of file
offset may be positive meaning move forwards or negative meaning move backwards. The
following examples illustrate the operation of the fseek function:
tatement Meaning
fseek(fp,0L,0) Go to beginning
fseek(fp, 0L, 1) Stays at current position
fseek(fp, 0L, 2) Go to end of the file, past the last character of the file
fseek(fp, m, 0) Move to (m+1)th byte in the file
fseek(fp, m, 1) Go forwared by m bytes
fseek(fp, -m, 1) Go backward by m bytes from the current position
fseek(fp, - m, 2) Go backward by m bytes from the end
ftell
ftell takes a file pointer and returns a number of type long that corresponds to the current
position. This function is useful in saving the current position of a file, which can be used later
in the program. It takes the following form
n = ftell(fp);
n would give the relative offset(in bytes) of the current position. This means that n bytes have
already been read (or written).
rewind takes a file pointer and resets the position to the start of the file.
for e.g.
rewind(fp);
n = ftell(fp);
n would return 0
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C LANGUAGE
Binary Mode
A file can be opened in binary mode as follows:
fp = fopen(“Poem. txt”, “rb”)
Here fp is file pointer
Poem. txt is file name
rb denotes that file is opened in binary mode for read operation.
Text Mode Versus Binary Mode:-
(i) New Lines:-
In text mode, a newline character is converted into the carriage return -linefeed combination
before being written to the disk. Like wise, the carriage return-line feed combination on the
disk is converted back in to a newline when the file is read by a c program. However if file is
opened in binary mode, as opposed to text mode, these conversions will not take place.
(ii) End of File:-
The difference is that in text mode when end-of-file is detected a special character whose
asciI value is 26, is inserted after the last character in the file to mark the end of file. If this
character is detected at any point in the file, the read function will return the EOF signal to the
program.
As against this, there is no such special character present in the binary mode files to mark the
end of file. The binary mode file keeps track of the end of file from the number of characters
present in directory entry of the file.
Text Mode:-
The only function available for storing in a disk file is the fprintf( ) in text mode. Here numbers
are stored as string of characters when written to the disk. These 1234, even though it occupies
two bytes in memory, when transferred to the disk using fprintf( ), it would occupy four
bytes, one byte per character. Similarly the floating point number 1234.56 would occupy 7
bytes on disk. These, numbers with more digits would require more disk space.
In binary by using the functions (fread( ) and fwrite( )) numbers are stored in binary format. It
means each number would occupy the same number of bytes on disk as it occupies in memory.
Command Line Arguments
Two special identifiers, argc and argv are used to pass to main( ) the number of command line
arguments and pointers to each argument we have to set up main( ) as follows.
main(int argc, char*argv[ ])
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C LANGUAGE
argc will then provide the number of command line arguments including the command itselfso
argC its never less than 1.
The argv is an array of pointer to char or equivalently an array of strings. Each of argv[0],
argv[1],... up to argv[argc-1] is a pointer to command line argument, namely a NULL terminated
string. The pointer argv[argc] is set to NULL to mark the end of the array.
Suppose these is a program Vkcpy in which main contains argument argc, and argv means
skeleton of program is as follows
main(int argc, char * argv[ ])
{ __________
__________
__________
__________
__________
}
suppose we now execute the program by typing VK COPY Hellow.C Hello.CBK Here argc =
3(command plus 2 arguments
argv[0] points to “C:\VKCPY\0”
argv[1] points to “HELLO.C\0”
argv[2] points to “HELLO.CBK\0”
argv[3] is NULL
ASSIMILATION EXERCISE
Q.1 Describe the different ways in which data files can be categorized in C.
Q.2 What is the purpose of library function feof ? . How the feof function be utilized within a
program that updates an unformatted data file
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C LANGUAGE
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C LANGUAGE
CHAPTER - 12
GRAPHICS FEATURES IN C
OBJECTIVES
At the end of this chapter, the user will be able to
* Differentiate graphics and text mode
* Play with different colors in the text mode
* Draw graphical figures in graphics mode
INTRODUCTION
In our day today life, the graphical figures such as tables, chairs, containers etc. are seen
more than the text. Hence it is thought to implement the graphical features in computers
which are widely used in many applications. The use of graphics is intended an adjunct to text
rather than being a substitute for text. Many computer languages such as BASIC, pascal, C
etc., supports the graphics features.
The applications of graphics are in the field of computer Aided Drafting (CAD), Computer
Aided Engineering (CAE), Computer Aided Instruction (CAI), Computer Aided Software Engineering
(CASE),
GRAPHICS IN C
ANSI standard C does not define any text screen of graphics functions because of the capabilities
of diverse hardware environments. But Turbo C version. 1.5 and higher support extensive
screen and graphics support facilities. In this chapter the features supported by Turbo C
are discussed.
MODE
Basically there are two different modes, namely text mode and graphics mode. in text mode,
as the name states, it is possible to display or capture only text in terms of ASCII. But in
Graphics mode, any type of figures can be displayed, captured and animated. Let us discuss
these features now.
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C LANGUAGE
(i) TEXT MODE
In Text mode, it is possible to handle, only the text which are present in ASCII. Text mode
display can be in two forms as 25 rows of 80 columns or 25 rows of 40 columns. The elements
of text are characters. Text mode can have 2 colors in monochrome monitor and 16 colors in
color monitor.
The printf ( ) function helps the text to be displayed on the monitor. but the following functions
help to present the text in an attractive manner. To execute these special functions conio.h
should be included in the program.
(i) textmode (int mode);
This function sets the number of rows and columns of the screen. the variable mode can take
the values 0, 1, 2, or 3.
0 represents 40 column black and white
1 represents 40 column color
2 represent 80 column black and white
3 represents 80 column color
Example :
/* sets to 80 columns color mode */
textmode (3);
(b) clrscr ( );
This function clears the entire screen and locates the cursor in the top left corner (1,1,)
(c) gotoxy (int x, int y);
This function positions the cursor to the location specified by x and y. x represents the row
number and y represents the column number
Example:
/* The following statement positions the cursor to 3rd row 4th column*/
gotoxy (3, 4);
(d) textbackground (int color);
This function gives the facility to Change the background color of the text mode. The valid
colors for the CGA are from 0 to 6 namely BLACK, BLUE, GREEN, CYAN, RED, MAGENTA
and BROWN.
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C LANGUAGE
Example:
/* background color is set to red*/
int col = 4;
textbackground (col)
(e) textcolor (int color);
This function sets the color in which the subsequent text is to be displayed. The supported
colors are numbered from 0 to 15 and 128 for blinking.
Example /* the subsequent display of text will be in brown*/
int colr = 6;
textcolor (colr);
(f) delline ( );
It is possible to delete a line of text and after the deletion all the subsequent lines will be
pushed up by one line.
Example:
\* deletes the 5th line *\
gotoxy (5,4);
delline ( );
(g) insline ( );
Inserts a blank line at the current cursor position.
Example:
gotoxy (3,5);
insline ( );
Example Program:
/* Program to display text using special functions*/
# include <conio.h>
main ( )
{
int n,m,;
/* clears the screen */
clrscr ( );
/* sets the text mode to 80 columns color*/
textmode (3);
/* SETS THE TEXT COLOR*/
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C LANGUAGE
textcolor (4);
/* sets the text background color */
textbackground (2);
/* Positions to 5th row and 14th column*/
gotoxy (5,15);
printf (“Enter two numbers:);
scanf (“%d %d”, &n, &m);
gotoxy (10,15);
printf (“Entered numbers are %d and %d \n\n”, n,m);
}
(ii) GRAPHICS MODE
In this mode it is possible to display text as well as graphical figures. The basic element of the
graphical pictures is picture element which is also called as pixel. The resolution of the monitor
is measured in terms of pixels and it varies with respect to the type of the monitor.
The monitor type can be monochrome, CGA, EGA, VGA, etc. Depending on the monitor type
and resolution, the graphics pictures and colors vary. Let us see some of the graphics functions
now. To execute these function “graphics.h” file should be included in the c program.
(a) initgraph (int *driver, int *mode, char *path);
This function is used to initialise the graphics system and load the appropriate specified graphics
driver and the video mode used by the graphics function. The path is to specify the place in
which the graphics driver files are available.
The driver is specified as 0 to 10 representing the monitor types DETECT, CGA, MCGA,
EGA, EGA64, EGAMONO, IBM8514, HERCMONO, ATT400, VGA and PC3270.
The mode specifies the resolution of the video. It can take the values as follows.
MODE VALUE RESOLUTION
CGAC0 0 320 X 200
CGAC1 1 320 X 200
CGAC2 2 320 X 200
CGAC3 3 320 X 200
CGAH1 4 640 X 200
The path specifies the system path from where the graphics driver files are to be searched.
If the files are in current directory then the path is a null string.
Whenever any graphics figure has to be drawn this intigraph ( ) function should be used to
initialise the graphics mode on the video.
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C LANGUAGE
Example:
int driver, mode;
driver =1;
mode = 4;
initgraph (&driver, &mode, “ “);
/* initialise driver to CGA mode to high resolution mode and the driver files are expected
to be present in the current directory */
(b) restorecrtmode ( );
This function restores the screen to the mode that it had prior to the call to initgraph ( ).
Example :
restorecrtmode ( ); \* restores back*\
(c) setpalatte (int index, int color);
This function chooses an index for palette and matches the color with the index and this color
sets the background color of CGA mode.
Example :
setpalette ( 0, GREEN);
\* Set the Background to Green*\
(d) Putpixel (int x, int y, int color);
This function illuminates the pixel represented by x and y coordinates in the color represented
by color
Example :
putpixel (10, 20, RED);
/* illuminates the pixel (10, 20) in red */
(e) getpixel (int x, int y);
This function returns the color in which the pixel (x,y) is illuminated
Example
color = getpixel (10, 20)
/* returns the color of the pixel (10, 20) */
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C LANGUAGE
(f) moveto (init x, int y);
This function moves cursor to (x, y) position.
Example
moveto (100, 150);
/* positions the cursor to (100, 150)*/
The following program illustrates the application of the above discussed functions.
It sets the graphics mode, illuminates a pixel in a colour and stores the colour of the pixel in
a variable.
EXAMPLE PROGRAM 95
# include <graphics.h>
main ( )
{
int driver, mode, colr;
driver = CGA;
mode = CGAC3
/* driver and modes are set */
initgraph (&driver, &mode, “ “);
/*graphics mode is initialized*/
setpalette (0, RED); /* sets palette*/
moveto ( 75, 100); /* moves to (75, 100)*/
putpixel (75, 100, RED); /* illuminates pixel (75, 100) in red */
colr = getpixel (75, 100);
/* colr holds the color number of RED which is the color of the pixel (75,100)*/
roatorecrtmode ( );
/* restores back to the mode prior to the invokation of graphics initialization*/
}
(g) lineto (int x, int y);
This function draws a line from the current cursor position to (x,y)
Example
lineto (150, 175);
/* draws line from current cursor to (150, 175)*/
(h) line (int x1, int y1, int x2, int y2)
This function draws a line from (x1,y1) to (x2, y2)
Example
line (10, 50, 10, 100);
/* draws a vertical line */
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C LANGUAGE
(i) bar (int x1, int y1, int x2, int y2);
This draws a rectangle with diagonal from (x1, y1) to (x2, y2);
Example
bar (10, 25, 100, 75);
/* Draws a rectangle with diagonal from (10,25) to (100, 75)*/
(j) bar3d (int x1, int y1, intx2, int y2, depth, topflag);
This function provides a 3 dimensional view of rectangle boxes. This draws a rectangle with
diagonal from (x1, y1) to (x2, y2) and with depth specified in the variable depth. If the top flag
is non zero, a top is added to the bar, and hence 3-Dimensional view is possible. Otherwise
the bar has no top.
The following program illustrates the application of the functions discussed above.
It displays rectangle along with two diagonals.
EXAMPLE PROGRAM 96
# include <graphics.h>
main ( )
{
int driver = CGA, mode, colr;
mode = CGAC3;
/* driver and modes are set*/
intigraph (&dirver, &mode, “ “);
/* graphics mode is initialized */
line (50, 40, 100, 80);
/*draws a line from (50,40) to (100, 80)*/
moveto (51, 41);
lineto (99, 79);
/* draws left diagonal */
moveto (99, 41);
lineto (51, 79);
/* draws right diagonal*/
restorecrtmode ( );
/* restores back to old mode */
}
(k) circle (int x, int y, int radius);
This function draws a circle centered at (x, y) with the radius specified by the variable radius
(in terms of number of pixels ) in the current drawing color.
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C LANGUAGE
Example
circle (100, 100, 50);
/* draws a circle with centre (100,100) and radius 50 */
(l) arc (int x, int y, int start, int end, int radius);
This function draws an arc of the circle with radius as specified in the variable radius and with
centre at (x, y). Start and end are given in degrees to mention the portion of the circle that
form the arc.
Example
arc (100, 100, 0, 90, 20);
/* draws the first quarter of the circle, arc with centre (100,100) and radius 20 pixels*/
(m) pieslice (int x, int y, int start, int end, int radius);
This function works in the same way as arc, but it provides the 2 radii from centre to start and
end.
Example
pieslice ( 100, 100, 90, 180, 50);
\* draws a pie with centre at (100, 100) and radius 50 pixels. The second quarter of the
circle is presented *\
(n) ellipse (int x, int y, int start, int end, int xrad, int yrad);
This function draws an ellipse with xrad as radius along x axis and yrad as radius along y axis.
The start and end should be 0 to 360 for full ellipse. Arcs of ellipse can also be drawn by
changing the start and end values as used in the function arc ( ).
Example
ellipse (100, 50, 0, 360, 30, 15);
/* draws full ellipse with centre at (100, 50), xradius 30 and yradius 15 */
(o) setcolor ( int color);
This function sets the drawing color as specified by the variable color. The subsequent graphical
figures will be in the color specified by the variable color.
Example
setcolor (4); /* sets the color to red */
The following program illustrates the application of the functions discussed above.
It displays a circle and ellipse drawn in different colors.
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C LANGUAGE
Example program 97:
# include <graphics.h>
main ( );
{
int driver, mode, colr;
driver = CGA;
mode = CGAC3;
/* driver and modes are set */
initgraph (&driver, &mode, “ “);
/* graphics mode is initialized*/
setcolor (3);
circle (50, 50, 25);
/* draws circle of radius 25 pircell and centre at (50, 50)*/
ellipse (50, 50, 0 360, 75, 50);
/* draws full ellipse with centre at (50, 50), x radius as 75 and y radius as 50 pixels in
color 5*/
restorecrtmode ( );
}
(p) setfillstyle (int pattern, int color);
This sets the pattern in which the closed boundaries can be filled and the color to fill the
boundary. The fixed patterns are represented by the values from 0 to 11
Example
setfillstyle (2, 5);
/* sets pattern to 2 and fill color as 5 */
(q) setfillpattern (char *pattern, int color);
This function helps the tiling or halftoning. This sets the pattern in which subsequent boundaries
can be filled. The pattern should be of 8 bits length.
Example
char p [9] = “ /2AB34CD
*p = “12AB 34CD”;
setfillpattern (p, RED)
/* set the pattern top */
(r) floodfill (int x, int y,int border);
Starting from the pixel (x,y) this function fills the area bounded by the color border. If the
boundary is not closed, then the entire screen is filled.
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C LANGUAGE
Example
setcolor (3);
circle (100, 100, 50);
floodfill (100, 100, 3);
/* fills the circle bounded by 3 */
(s) setlinestyle (int style, unsigned pattern, int width);
This function determines the way the subsequent lines should look. Style can be any one of
SOLID_LINE, DOTTED_LINE, CENTRE_LINE, DASHED _LINE, USERBIT_LINE. The width
can be NORM_WIDTH or THICK_WIDTH. The pattern should be specified for USERBIT_LINE.
Example
unsigned p = 11101101;
setlinestyle (CENTRE_LINE, 0, NORM_WIDTH);
lineto (100, 150);
/* Draws a styled line from current position to (100, 150) */
setlinestyle (USERBIT _LINE, p, NORM_WIDTH);
lineto (200, 190);
/* Draws a styled line specified by the user from current position to (100, 190)*/
(t) outtext (string);
In graphics mode user text can also be printed at the specified location by outtext.
Example
outtext (10, 10, “graphics mode text”);
/* displays text at (10,10)*/
(u) cleardevice ( );
This function clears the screen in graphics mode.
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C LANGUAGE
Example Program 98:
/* Program to display concentric circles*/
# include <graphics.h>
main ( )
{
int driver, mode, i;
driver = CGA;
mode = CGAC3
/* driver and modes are set */
initgraph (&driver, &mode, “ “)
/*graphics mode is initialized*/
setcolor (3);
for ( i = 25, i < 150, i+= 25)
circle (50, 50, i);
/* draws concentric circle of radius i pixels and centre at (50, 50) in color 3 */
restorecrtmode ( );
/* restores back to old mode */
}
ASSIMILATION EXERCISE
Q.1 What is difference between textmode and graphics mode
Q.2 Write a program to generate the following figure.
Q.3 Write C program using graphics to draw the following figures :