poj 1942 Paths on a Grid 求组合数mCn的方法

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unsigned int comb(unsigned a,unsigned b)
{
if(b > a-b)
b= a-b;

double result = 1;

while(b>0)
{
result *= (double)a / (double) b;

//cout<<"result:"<<result<<endl;
--a;
--b;
}

return ( unsigned int)(result + 0.5); //四舍五入
}
一个求组合数的函数

 #include <iostream> #include <stdio.h>  using namespace std;  //C(a,b) // unsigned int comb(unsigned  a,unsigned  b) {         if(b > a-b)                 b= a-b;          double result = 1;                  while(b>0)         {                 result *= (double)a / (double) b;                                  //cout<<"result:"<<result<<endl;                 --a;                 --b;         }                         return ( unsigned int)(result + 0.5); }         int main() {         unsigned int m,n;         while(cin>>m>>n)         {                 if(m==0&&n==0)                         break;                                          cout<<comb(m+n,m)<<endl;         }        }