Types of User-defined Functions in C Programming
Types of User-defined Functions in C Programming
In this tutorial, you will learn about different approaches you can take to solve the same problem using functions.
Posted By Manisha Gupta
These 4 programs below check whether the integer entered by the user is prime number or not. The output of all these programs below is same, and we have created a user-defined function in each example. However, the approch we have taken in each example is different.
Example 1: No arguments passed and no return Value
#include <stdio.h>
void checkPrimeNumber();
int main()
{
checkPrimeNumber(); // argument is not passed
return 0;
}
// return type of the function is void because function is not returning anything
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;
n = getInteger(); // no argument is passed
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;
}
int getInteger() // returns integer entered by the user
{
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)
{
int i;
for(i=2; i <= n/2; ++i)
{
if(n%i == 0)
return 1;
}
return 0;
}
The input from the user is passed to
checkPrimeNumber() function.
The
checkPrimeNumber() function checks whether the passed argument is prime or not. If the passed argument is a prime number, the function returns 0. If the passed argument is a non-prime number, the function returns 1. The return value is assigned to the flag variable.
Depending on whether flag is 0 or 1, appropriate message is printed from the
main()function.Which approach is better?
Well, it depends on the problem you are trying to solve. In this case, passing argument and returning a value from the function (example 4) is better.
A function should perform a specific task. The
checkPrimeNumber() function doesn't take input from the user nor it displays the appropriate message. It only checks whether a number is prime or not, which makes code your code easy to understand and debug.
