C function argument and return values

In C programming, functions can be categorized based on two criteria: whether they accept arguments (parameters) and whether they return a value. This gives us four distinct types of functions that cover all possible combinations.

Syntax

return_type function_name(parameter_list) {
    // Function body
    return value; // Optional, depends on return_type
}

Types of Functions

• Function with no arguments and no return value − Takes no input and returns nothing (void)
• Function with no arguments but returns a value − Takes no input but returns a value
• Function with arguments but no return value − Takes input parameters but returns nothing (void)
• Function with arguments and return value − Takes input parameters and returns a value

Example 1: No Arguments, No Return Value

This function takes no parameters and returns nothing −

#include <stdio.h>

void my_function() {
    printf("This is a function that takes no argument, and returns nothing.");
}

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

This is a function that takes no argument, and returns nothing.

Example 2: No Arguments, Returns Value

This function takes no parameters but returns an integer value −

#include <stdio.h>

int my_function() {
    printf("This function takes no argument, but returns 50<br>");
    return 50;
}

int main() {
    int x;
    x = my_function();
    printf("Returned Value: %d", x);
    return 0;
}

This function takes no argument, but returns 50
Returned Value: 50

Example 3: Takes Arguments, No Return Value

This function accepts an integer parameter but returns nothing −

#include <stdio.h>

void my_function(int x) {
    printf("This function is taking %d as argument, but returns nothing", x);
}

int main() {
    int x = 10;
    my_function(x);
    return 0;
}

This function is taking 10 as argument, but returns nothing

Example 4: Takes Arguments and Returns Value

This function accepts an integer parameter and returns its squared value −

#include <stdio.h>

int my_function(int x) {
    printf("This will take an argument, and will return its squared value<br>");
    return x * x;
}

int main() {
    int x, res;
    x = 12;
    res = my_function(x);
    printf("Returned Value: %d", res);
    return 0;
}

This will take an argument, and will return its squared value
Returned Value: 144

Key Points

• Use void as return type when function doesn't return any value
• Empty parentheses () indicate no parameters
• Functions with return values must use return statement

Conclusion

Understanding these four function types helps in designing modular C programs. Choose the appropriate type based on whether your function needs input data and whether it should produce output for the calling code.