The document discusses functions in C programming. It covers function prototypes, different types of functions based on return type and arguments, recursive functions, and examples of implementing various functions. It also covers preprocessor directives like file inclusion and macro substitution.

1. CHAPTER 6
Function
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2. Function prototype
The declaration of a function before using it in
the program is called function prototype. It
tells the compiler in advance about some
characteristics of the function(name of the
function) return type, parameter, etc.
The general format of function prototype is
return type.
Datatype function_name(type arg1, type arg2);
int add(int x, int y);
int add(int x, int, float);
int add();
void add(int, float);
void add();
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3. Classification of function according to
return type and argument:
1. Function with no argument and no return
type
2. Function with argument but no return type
3. Function with argument and return type
4. Function with no argument but with return
type
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4. Function with no argument and no
return type
When a function has no arguments the called
function does not receive any value from the
calling function. Similarly, when the called
function does not return any value , the calling
function does not receive any value from the
called function.
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5. #include<stdio.h>
void circleArea(); // function prototype
main() // Main function
{
circleArea();
}
void circleArea() //user defined function
{
float area;
float radius;
printf("Enter the radius : n");
scanf("%f",&radius);
area = 3.14 * radius * radius ;
printf("Area of Circle is %f",area);
}
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6. Function with argument but no
return type
When a function has arguments, it receives
data from the calling function but when it
does not return any value , the calling function
does not receive any data from the called
function.
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7. #include<stdio.h>
void areaCircle(float rad);
main()
{
float radius;
printf("Enter the radius : n");
scanf("%f",&radius);
areaCircle(radius);
}
void areaCircle(float rad)
{
float ar;
ar = 3.14 * rad * rad ;
printf("Area of Circle = %f",ar);
}
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8. Function with argument and return
type
When a function has arguments the called
function receives data from the calling
function. Similarly, when it returns a value ,
the calling function receives data from the
called function.
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9. #include <stdio.h>
float circleArea(int);
main()
{
int radius;
float a;
printf("Enter the radius of the circle ");
scanf("%d",&radius);
a = circleArea(radius);
printf("n Area of Circle is %f ",a);
}
float circleArea(int r)
{
float area;
area = 3.14 * r * r;
return(area);
}
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10. Function with no argument but with
return type
When a function has no arguments the calling
function does not receive any value from the
calling function but when it returns a value ,
the calling function receive any data from the
called function.
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11. #include<stdio.h>
int areaCircle();
main()
{
float a;
a= areaCircle();
printf("n Area of Circle is %f ",a);
}
int areaCircle()
{
float ar;
float radius;
printf("Enter the radius : n");
scanf("%f",&radius);
ar = 3.14 * radius * radius ;
return ar;
}
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12. Recursive Function:
Recursion is a programming technique that
allows the programmer to express operations
in terms of themselves. It is a programming
method in which function call itself.
Two important condition must be satisfied by
any recursive function and they are:
1. Each time a function call itself, it must be
closer to the solution.
2. There must be decision criteria for stopping
the process which is also called base criteria.
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13. Example: Factorial of a Number Using
Recursion
#include <stdio.h>
long int fact(int n);
int main()
{
int n;
printf("Enter a positive number: ");
scanf("%d", &n);
printf("Factorial of %d = %ld", n, fact(n));
return 0;
}
long int fact(int n)
{
if (n >= 1)
return n*fact(n-1);
else
return 1;
}
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14. Example: Fibonacci series upto nth terms Using Recursion
#include<stdio.h>
int Fibonacci(int);
int main()
{
int n, i;
scanf("%d",&n);
printf("Fibonacci seriesn");
for ( i = 0 ; i <= n ; i++ )
{
printf("%dn", Fibonacci(i));
}
return 0;
}
int Fibonacci(int n)
{
if ( n == 0 )
return 0;
else if ( n == 1 )
return 1;
else
return ( Fibonacci(n-1) + Fibonacci(n-2) );
}
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15. Example: Sum of n natural number using recursion
#include <stdio.h>
int sum (int num);
int main()
{
int num, result;
printf("Enter the number: ");
scanf("%d", &num);
result = sum (num);
printf("Sum of %d natural number is %dn", num, result);
return 0;
}
int sum (int num)
{
if (num != 0)
{
return (sum (num-1)+num);
}
else
{
return 0;
}
}
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16. Example: Sum of digits of a given number using recursion
#include <stdio.h>
int sumDigit (int num);
int main()
{
int num, result;
printf("Enter the number: ");
scanf("%d", &num);
result = sumDigit(num);
printf("Sum of digits in %d is %dn", num, result);
return 0;
}
int sumDigit (int num)
{
if (num != 0)
{
return (num % 10 + sumDigit (num / 10));
}
else
{
return 0;
}
}
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17. Example: reverse a given number using recursive function
#include<stdio.h>
int revFunct(int num);
int main(){
int num,revNum;
printf("Enter any number: n");
scanf("%d",&num);
revNum=revFunct(num);
printf("After reverse the number is :%d n",revNum);
return 0;
}
int rev=0,rem;
revFunct(int num){
if(num){
rem=num%10;
rev=rev*10+rem;
revFunct(num/10);
}
else
return rev;
return rev;
}
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18. Src:https://www.geeksforgeeks.org/storage-classes-in-c/
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19. PRE PROCESSOR DIRECTIVE
The pre processor is a program that process
the source code before it passes through the
compiler. It begins with a ’#’ symbol. The
directive is most often placed at the beginning
of the program before the main function. It
can be classified into two types:
1. File inclusion directive
2. Macro substitution directive
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20. 1. File Inclusion directive
This directive can cause one file to be included in
another. The file contains function and macro
definition. The general form of pre-processor
command for file inclusion is :
# include “ file name “
where filename is the name of the file containing
the required definition or function. At this point,
the pre-processor inserts the entire content of
the filename into the program.
Eg:
# include “myfile.c”
# include < myfile.c>
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21. 2. Macro substitution directive
It is the process where an identifier in a program is
replaced by a pre-defined string composed of one or more
tokens. This process performs the task under the direction
of predefined statement . They take the general form as:
# define identifier value
Eg: # define PI 3.7415
These are of 3 types:
a. Simple macro substitution
b. Argumented macro substitution
c. Nested macro substituton
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22. a. Simple macro substitution
Simple string replacement is used to define a constant.
#include <stdio.h>
#define num 5
int main()
{
int i ;
float average,arr[n],sum=0;
for (i=0;i<num;i++)
{
scanf("%f",&arr[i]);
sum=sum +arr[i];
}
average= sum/num;
printf ("sum = %f",sum);
printf ("average = %f",average);
return 0;
}
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23. b. Argumented macro substitution
This pre-processor permits us to define macro in more
complex and uniform useful form. The general form is:
# define identifier( a1,a2,a3,......an) expression
where a1,a2,a3,......an are formal macro argument which
are analogous to formal argument in a function definition
There is no space between identifier and opening
parenthesis, string behave like a template.
Subsequent occurrence of a macro call which is analogous
to the function call.
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24. //Example program to find area of a circle
# include <stdio.h>
# define AREA(r) (3.14*r*r)
main()
{
float radius , area ;
printf ("Enter radius");
scanf ("%f",& radius);
area= ( AREA(radius));
printf ( "Area = %f",area);
}
//or alternative program
#include <stdio.h>
#define area(r) (3.141*r*r)
int main()
{
float r=2;
printf("area is %f",area(r));
}
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25. c. Nested macro substitution
One macro can be used in the definition of another macro.
Eg :
# include <stdio.h>
# define N 5
# define LOOP for (i=0; i <N;i++)
main()
{
int i, arr [N], sum=0;
float average;
LOOP
{
scanf("%d",&arr[i]);
sum = sum + arr[i];
}
average = (float)sum /N;
printf ("sum=%f",average);
}
Here macro N is used inside the macro LOOP
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26. Assignment
1. Define function, function definition, function call
,function declaration with example.
2. WAP to find the sum of all the prime numbers in a
given array. The main function should take the help of
user defined function that tests whether the given
number is prime or not.
3. WAP to input a number and find the sum of its digits
using recursive function.
4. Write notes on:
• preprocessor directives
• storage class
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