例1-1

#include<stdio.h>
int main(void)
{
    int n;
    int factorial(int n);

    scanf_s("%d",&n);
    printf("%d\n",factorial(n));

    return 0;
}
int factorial(int n)
{
    int i,fact=1;

    for(i=1;i<=n;i++)
        fact=fact*i;

    return fact;
}