Send a value back to main

A points calculator can give a value back to its caller. When main reaches double_points(4), the call passes 4 into points. The function computes 8 and returns it; main uses that value to initialize result, then continues. A returned value does not print by itself.

Follow the diagram from main into double_points with argument 4, then back with 8. points belongs to the called function; result belongs to main. The return ends this call, and main picks up where it left off.

Start reading at main and predict the line it prints:

#include <stdio.h>

int double_points(int points) {
    int doubled = points * 2;
    return doubled;
}

int main(void) {
    int result = double_points(4);
    printf("Result: %d\n", result);
    return 0;
}

Try double_points(6) and check the printed result. You can also use a returned value directly in a larger expression:

#include <stdio.h>

int add_fee(int amount) {
    return amount + 2;
}

int main(void) {
    int bill = add_fee(5) * 2;
    printf("Bill: %d\n", bill);
    return 0;
}

add_fee(5) yields 7, then multiplication makes bill 14. For the earlier example, you can trace the same handoff: main waits at double_points(4) while points becomes 4 and doubled becomes 8; return doubled; gives 8 back. return 0; in main reports an exit status instead. Neither return displays anything. That job belongs to printf.