程序代码：

#include<stdio.h>
#include<stdlib.h>
int main()
{
    int i = 0;/* i为计数器 */
    int n;
    int factorial = 1;/* 保存阶乘的结果 */
    puts("*************************************");
    puts("*      The program will compute     *");
    puts("*    the factotial of an integer    *");
    puts("*************************************");
    puts("please input the number n:");
    scanf("%d",&n);
    if(n < 0)/*判断输入的书是否大于或等于0*/
    {
          printf("please input an interger >= 0.\n");
        return 0;
    }
    if(n==0)/* 0的阶乘是1 */
    {
        printf("factorial of 0 is 1.\n");
        return 0;
    }
    i = 1;
    while(i <= n)
    {
        factorial = factorial * i;
        i++;
    }
    printf("factorial of %d is:%d.\n",n,factorial);
    getch();
    return 0;
  
}