What is the difference between call by value and call by reference in C?

In call by value the function gets a copy of the variable, so the original value does not change. In call by reference we pass the address (a pointer), so the function can change the original value.

#include <stdio.h>

void byValue(int n)    { n = 100; }
void byAddress(int *n) { *n = 100; }

int main(void) {
    int a = 1, b = 1;
    byValue(a);
    byAddress(&b);
    printf("%d %d\n", a, b);
    return 0;
}

Output:

See the full chapter Call by Value and Reference.

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