C Functions

programming C MOC

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Functions in C require the return value of the function. void indicates nothing is returned.

Variables defined in functions have local scope, so changes are only reflected in the function.

#include <stdio.h>
 
void add5(int n) {
    n += 5;
    printf("%d\n", n);
}
 
int main() {
    int num = 0;
 
    add5(num);                 // 5
    printf("%d\n", num);       // 0
    add5(num);                 // 5
    printf("%d\n", num);       // 0
    num += 2;
    printf("%d\n", num);       // 2
    add5(num);                 // 7
    printf("%d\n", num);       // 2
 
    return(0);
}

Arguments by Reference

Values passed into a function are copies, to affect the original values, pass pointers.

#include <stdio.h>
 
void add5(int *n) {
    *n += 5;
    printf("%d\n", *n);
}
 
int main() {
    int num = 0;
 
    add5(&num);               // 5
    printf("%d\n", num);      // 5
    add5(&num);               // 10
    printf("%d\n", num);      // 10
    num += 2;
    printf("%d\n", num);      // 12
    add5(&num);               // 17
    printf("%d\n", num);      // 17
 
    return(0);
}

Function Pointers

Pointers can even point to functions.

#include <stdio.h>
 
void say_hello() {
    puts("Hello from the function");
}
 
int main() {
    void (*pf)();
    pf = &say_hello;
    pf();
 
    return(0);
}