Reverse numbers

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int num = 0, length = 1, Rnum = 0;
    scanf("%i", &num);
    if(num < 0)
    {
        num *= -1;
    }

    printf("reverse: ");

    while(num >= 1)
    {
        printf("%i", num % 10);
        Rnum += num * length;
        length  *= 10;
        num /= 10;
    }
}