求阶乘n！

1. 递推法

#include 
long fac(int n) 
{
     int i;
     long fact=1;
     for(i=1;i<=n;i++) 
	        fact=fact*i;
     return fact;
}
void main()
{ long fac(int n); 
   int n;
   long fact=0; 
   printf("input an integer number:"); 
   scanf("%d",&n); 
   fact=fac(n); 
   printf("%d!=%ld\n",n,fact); 
}
 

2.递归法

#include <stdio.h>
long fac(int n)
{
    long f;
    if (n < 0)
        printf("data error!");
    else if (n == 0 || n == 1)
        f = 1;
    else  f = n * fac(n - 1);
    return(f);
}
void  main()
{
    long fac(int n);
    int n, fact;
    printf("input an integer number:");
    scanf("%d", &n);
    fact = fac(n); 
    printf("%d!=%ld\n", n, fact);
}