C Call by Value and Call by Reference

There are two ways to pass arguments to a function.

Call by value

A copy of the value is sent. Changes inside the function do not change the original variables. C uses this way by default.

#include <stdio.h>

void swap(int a, int b) {
    int t = a;
    a = b;
    b = t;
}

int main(void) {
    int x = 10, y = 20;
    swap(x, y);
    printf("x=%d y=%d\n", x, y);
    return 0;
}

Output:

The values did not swap, because the function worked on copies.

Call by reference (using pointers)

We send the address of the variables with &. The function uses pointers (*) to change the original values.

#include <stdio.h>

void swap(int *a, int *b) {
    int t = *a;
    *a = *b;
    *b = t;
}

int main(void) {
    int x = 10, y = 20;
    swap(&x, &y);
    printf("x=%d y=%d\n", x, y);
    return 0;
}

Output:

Difference

Point	Call by value	Call by reference
What is sent	Copy of the value	Address of the variable
Original changed?	No	Yes
Memory	Extra copy is made	No copy of the data

Next: C Recursion.

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