Programs on Functions.

Example: User-defined function

Here is a example to add two integers. To perform this task, a user-defined function addNumbers() is defined.

#include <stdio.h>

int addNumbers(int a, int b);         // function prototype

int main()
{
    int n1,n2,sum;

    printf("Enters two numbers: ");
    scanf("%d %d",&n1,&n2);

    sum = addNumbers(n1, n2);        // function call

    printf("sum = %d",sum);

    return 0;
}

int addNumbers(int a,int b)         // function definition   
{
    int result;
    result = a+b;
    return result;                  // return statement
}

Example #1: No arguments passed and no return Value

#include <stdio.h>

void checkPrimeNumber();

int main()
{
    checkPrimeNumber();    // no argument is passed to prime()
    return 0;
}

// return type of the function is void becuase no value is returned from the function
void checkPrimeNumber()
{
    int n, i, flag=0;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    for(i=2; i <= n/2; ++i)
    {
        if(n%i == 0)
        {
            flag = 1;
        }
    }
    if (flag == 1)
        printf("%d is not a prime number.", n);
    else
        printf("%d is a prime number.", n);
}

The checkPrimeNumber() function takes input from the user, checks whether it is a prime number or not and displays it on the screen.

The empty parentheses in checkPrimeNumber(); statement inside the main() function indicates that no argument is passed to the function.

The return type of the function is void. Hence, no value is returned from the function.

Example #2: No arguments passed but a return value

#include <stdio.h>
int getInteger();

int main()
{
    int n, i, flag = 0;

    // no argument is passed to the function
    // the value returned from the function is assigned to n
    n = getInteger();

    for(i=2; i<=n/2; ++i)
    {
        if(n%i==0){
            flag = 1;
            break;
        }
    }

    if (flag == 1)
        printf("%d is not a prime number.", n);
    else
        printf("%d is a prime number.", n);

    return 0;
}

// getInteger() function returns integer entered by the user
int getInteger()
{
    int n;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    return n;
}

The empty parentheses in n = getInteger(); statement indicates that no argument is passed to the function. And, the value returned from the function is assigned to n.

Here, the getInteger() function takes input from the user and returns it. The code to check whether a number is prime or not is inside the main() function.

Example #3: Argument passed but no return value

#include <stdio.h>
void checkPrimeAndDisplay(int n);

int main()
{
    int n;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    // n is passed to the function
    checkPrimeAndDisplay(n);

    return 0;
}

// void indicates that no value is returned from the function
void checkPrimeAndDisplay(int n)
{
    int i, flag = 0;

    for(i=2; i <= n/2; ++i)
    {
        if(n%i == 0){
            flag = 1;
            break;
        }
    }
    if(flag == 1)
        printf("%d is not a prime number.",n);
    else
        printf("%d is a prime number.", n);
}

The integer value entered by the user is passed to checkPrimeAndDisplay() function.

Here, the checkPrimeAndDisplay() function checks whether the argument passed is a prime number or not and displays the appropriate message.

Example #4: Argument passed and a return value

#include <stdio.h>
int checkPrimeNumber(int n);

int main()
{
    int n, flag;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    // n is passed to the checkPrimeNumber() function
    // the value returned from the function is assigned to flag variable
    flag = checkPrimeNumber(n);

    if(flag==1)
        printf("%d is not a prime number",n);
    else
        printf("%d is a prime number",n);

    return 0;
}

// integer is returned from the function
int checkPrimeNumber(int n)
{
    /* Integer value is returned from function checkPrimeNumber() */
    int i;

    for(i=2; i <= n/2; ++i)
    {
        if(n%i == 0)
            return 1;
    }

    return 0;
}