DS – Functions in C

Variable: Stores data.

Function: Performs operation on data.

Function takes input, performs operations and returns output

SyntaxExample
int identity(arguments)            
{                        
-> statements;            
}		int add(int a, int b)            
{                        
int res = a+b ;                        
return res ;            
}

C functions classified into:

  • Built In Functions
  • User Defined Functions

Built in Functions:

  • C library is a set of header files
  • Header file is a collection of pre-defined functions.
stdio.hconio.hstring.hgraphics.h
printf()
scanf()
feof()
…		getch()
clrscr()
getche()
….		strlen()
strrev()
strcat()
…..		line()
circle()
bar()
…

Custom Functions: Programmed defined functions based on application requirement

Calculator.cMobile.cAccount.c
add()
subtract()
multiply()
divide()		call()
message()
store()
…..		deposit()
withdraw()
….

Every function consists

  • Prototype:
    • Prototype is called function declaration. Every Custom function must be specified before main().
  • Definition:
    • Definition is a block of instructions contains function logic. Function executes when we call that function.
  • Function call:
    • It is a statement and it is used to execute the function logic.

No arguments and No return values function:

#include<stdio.h>
void sayHi(void);
int main(void)
{
            sayHi();
            return 0 ;         
}
void sayHi(void)
{
            printf(“Hi to all \n”);
}

With arguments and No return values function: (Even Number Program)

#include<stdio.h>
void isEven(int);
int main(void)
{
            int n;
            printf(“Enter number : “);
            scanf(“%d”, &n);
            isEven(n);
            return 0 ;         
}
void isEven(int num){
            if(num%2==0)
                        printf(“%d is Even \n”, num);
            else
                        printf(“%d is not Even \n”, num);
}

With arguments and With return values function: (addition of 2 numbers)

#include <stdio.h>
int add(int, int);
int main()
{
            int a, b, res;
            printf(“Enter two numbers : \n”);
            scanf(“%d%d”, &a, &b);
            res = add(a,b);
            printf(“%d + %d = %d\n”, a, b, res);
            return 0;
}
int add(int x, int y)
{
            int z=x+y ;
            return z;
}

No arguments and With return values function:

float getPI(void);
void main(void)
{
            float pi;
            fpi = getPI();
            printf(“PI value is : %f\n”, pi);
}
float getPI(void){
            return 3.142;
}

Arithmetic Operations Menu Driven program – Using functions

#include <stdio.h>
float add(float,float);
float subtract(float,float);
float multiply(float,float);
float divide(float,float);
int main()
{
            int choice;
            float a,b,c;
            while(1)
            {
                        printf(“1.Add\n”);
                        printf(“2.Subtract\n”);
                        printf(“3.Multiply\n”);
                        printf(“4.divide\n”);
                        printf(“5.Exit\n”);
                        printf(“Enter your choice : “);
                        scanf(“%d” , &choice);
           
                        if(choice>=1 && choice<=4)
                        {
                                    printf(“Enter 2 numbers :\n”);
                                    scanf(“%f%f”, &a, &b);
                        }
           
                        switch(choice)
                        {
                                    case 1  :           c = add(a,b);
                                                            printf(“Result : %f\n\n”,c);
                                                            break ;
                                    case 2  :           c = subtract(a,b);
                                                            printf(“Result : %f\n\n”,c);
                                                            break ;
                                    case 3  :           c = multiply(a,b);
                                                            printf(“Result : %f\n\n”,c);
                                                            break ;
                                    case 4  :           c = divide(a,b);
                                                            printf(“Result : %f\n\n”,c);
                                                            break ;
                                    case 5  :           exit(1);
                                    default :           printf(“Invalid choice \n\n”);
            }
    }
    return 0;
}
float add(float x, float y)
{
            return x+y ;
}
float subtract(float x, float y)
{
            return x-y ;
}
float multiply(float x, float y)
{
            return x*y ;
}
float divide(float x, float y)
{
            return x/y ;
}

Recursion:

  • Function calling itself.
  • Calling the function from the definition of same function
#include<stdio.h>
void recur();
int main()
{
            recur();            
            return 0;
}
void recur()
{
            printf(“Start\n”);
            recur();
            printf(“End\n”);
}

We need to take care of function execution completion in recursive call.

#include<stdio.h>
void abc(int);
int main()
{
            abc(3);             
            return 0;
}
void abc(int x)
{
            printf(“x : %d\n”,x);
            if(x>0)
                        abc(x-1);
}
#include<stdio.h>
void abc(int);
int main()
{
            abc(3);             
            return 0;
}
void abc(int x){
            printf(“x : %d\n”,x);
            if(x>0)
                        abc(x-1);
            printf(“x : %d\n”,x);
}

Find the factorial using recursion:

#include<stdio.h>
int fact(int);
int main()
{
            int res;
            res = fact(4);
            printf(“Factorial : %d \n”, res);             
            return 0;
}
int fact(int n)
{
            if(n==0)
                        return 1;
            else
                        return n*fact(n-1);
}

Program to find sum of first N numbers using Recursion:

#include<stdio.h>
int sum(int);
void main(void)
{
            int n, s;
            printf(“Enter n value : “);
            scanf(“%d”, &n);
            s = sum(n);
            printf(“Sum of %d nums : %d\n”, n, s);
}
int sum(int n)
{
            if(n==0)
                        return n;
            else
                        return n+sum(n-1);
}
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