Factorial

#include <stdio.h>

void main()
{
    int arg;
    Loop: scanf("%d", &arg);
    printf("%d", fat(arg));
    goto Loop;
}

int fat(int n)  //Receives an integer as input and returns it's factorial. If the input is invalid, returns the input itself. Time complexity of O(n)
{
    if (n == 0)
        return 1;
    int i;
    for (i = n - 1; i > 0; i--)
        n = n * i;
    return n;
}