排列組合：數學公式求解

#include<stdio.h>
double Count(int n);
int main()
{
	int n,m;
    double Above,Below,x;
    double Count(int n);
    printf("Enter n and m(m<=n):\n");
    scanf("%d,%d",&n,&m);
    Above=Count(n);
    Below=Count(m);
    x=Count(n-m);
    printf("%0.1f\n",Above/(Below*x));
}
double Count(int n)//求階乘
{
    int i;
    double sum;
    sum=1;
    for(i=1;i<=n;i++)
    {
    	sum=sum*i;
    }
    return sum;
}
/*
（樣例輸入）
Enter n and m(m<=n):
5 3
10.0
*/