Why is temp used in this?

Question

#include <stdio.h>

void swap (int *num1, int *num2);

int main() {
int x = 25;
int y = 100;

printf("x is %d, y is %d\n", x, y);
swap(&x, &y);
printf("x is %d, y is %d\n", x, y);

return 0;
}

void swap (int *num1, int *num2) {
int temp;

temp = *num1;
*num1 = *num2;
*num2 = temp;
}

Answer 1

It is a temporary variable which is just used for swapping two values but is not required later.

Answer 2

Try what happens without using "temp":

*num1 = *num2; // ok, num1 has now the value of num2
*num2 = ???; // ooops, we have overwritten the previous value of num1