Call by Value and Call by Reference

C passes copies of arguments; to let a function modify a variable, pass its address with a pointer.

Easy

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

int x = 1, y = 2;
swap(&x, &y);     // x = 2, y = 1

C is strictly call by value: the function receives copies. Passing a pointer copies the address, which lets the function reach the original variable — this is how C emulates call by reference. Arrays are passed as pointers to their first element.

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