用逆推和递归的方式求n!

用逆推和递归的方式求n!

1. 用逆推方法求n！，从1开始一直乘到n

#include <stdio.h>                  
void main()
{//system("mode con cp select=65001");long fac(int n);int n;long fact=0;printf("请输入n的值:");scanf("%d",&n);fact=fac(n);printf("%d!=%dn",n,fact);
}
long fac(int n){int i;long fact=1;for(i=1;i<=n;i++){fact=fact*i;}return fact;
}

2. 用递归的方法求n！

• n=0,1时，n!=1

• n>1时，n!=n*(n-1)!

#include <stdio.h>                  
void main()
{//system("mode con cp select=65001");long fac(int n);int n,y;long fact=0;printf("请输入n的值:");scanf("%d",&n);y=fac(n);printf("%d!=%dn",n,y);
}
long fac(int n){long f;if(n<0){printf("n<0,data error!");}else if(n==0 || n==1){f=1;}else{f=fac(n-1)*n;}return(f);
}