Different Categories of Functions in C Programming

Functions are categorized bases on the presence or absences of arguments and whether they return a value. A user-defined function is one that is defined by the user when writing any program, as opposed to library functions that have predefined definitions.

To meet specific requirements, the user must develop their own functions. Such functions must be properly defined by the user. A function is a block of code designed to perform a specific task. It is written once and can be reused multiple times as needed by the programmer.

• Functions without arguments but with return values.

• Functions without arguments but with return values.

• Functions with arguments but without return values

• Functions with arguments but with return values.

Functions without arguments but without return values

When a function has no arguments, it does not receive any data from the calling function. Similarly, when a function does not return a value, the calling function does not receive any data from the called function.

Example

This code defines a sum function that takes no arguments, reads two integers from the user, calculates their sum, and prints the result. The main function calls sum.

#include <stdio.h>

void sum();

int main() {
   sum();
   return 0;
}

void sum() {
   int a, b, c;
   printf("Enter 2 numbers: ");
   scanf("%d%d", &a, &b);
   c = a + b;
   printf("Sum = %d", c);
}

The result is generated as follows &minus

Enter 2 numbers:
3
5
Sum=8

Functions without arguments and with return values

Here is an example of creating functions that do not take any arguments but return a value to calling function. For instance, the getchar function has no parameter but returns an integer representing a character.

Example

Here, the code demonstrates a sum function that takes no arguments, reads two integers from the user, calculates their sum, and returns the result. The main function calls sum and prints the sum.

#include <stdio.h>

int sum();

int main() {
   int c;
   c = sum();
   printf("Sum = %d", c);
   return 0;
}

int sum() {
   int a, b, c;
   printf("Enter 2 numbers: ");
   scanf("%d %d", &a, &b);
   c = a + b;
   return c;
}

We will get the output as follows ?

Enter two numbers 10 20
30

Functions with arguments and without return values

When a function has arguments, this receives any data from the calling function but with no return value. These are void functions with no return values.

Example

This code reads two integers, calculates their sum using the sum function, and prints the result.

#include <stdio.h>

void sum(int, int);

int main() {
   int a, b;
   printf("Enter 2 numbers: ");
   scanf("%d%d", &a, &b);
   sum(a, b);
   return 0;
}

void sum(int a, int b) {
   int c;
   c = a + b;
   printf("Sum = %d", c);
}

The output is obtained as follows ?

Enter two numbers 10 20
Sum=30

Functions with arguments and with return values

This function takes an integer argument, performs some operations, and returns the integer value. This demonstrates the basic function usage in C.

Example

This code demonstrates two integers, calculates their sum using sum function, and prints the result. The main function specifies the input and output, while sum performs the addition.

#include <stdio.h>

int sum(int, int);

int main() {
   int a, b, c;
   printf("Enter 2 numbers: ");
   scanf("%d%d", &a, &b);
   c = sum(a, b);
   printf("Sum = %d", c);
   return 0;
}

int sum(int a, int b) {
   int c;
   c = a + b;
   return c;
}

The result is generated as follows ?

Enter two numbers 10 20
Sum=30