4.2分别使用循环和递归两种策略求二项式从c(n,k);

//4.2分别使用循环和递归两种策略求二项式从c(n,k);
//以for循环运行c(n,k)
#include <iostream>
using namespace std;
int sum(int m);
int main()
{
int n,k;
int sum_n,sum_k,sum_i,sum_n_k;
cout<<"请输入C(n,k)中的n值："<<endl;
cin>>n;
cout<<"请输入C(n,k)中的k值："<<endl;
cin>>k;
if(n<k)
{
cout<<"error,please input again."<<endl;
return 0;
}
sum_n=sum(n);
sum_k=sum(k);
sum_i=sum(n-k);
sum_n_k=sum_n/(sum_k*sum_i);
cout<<"C(n,k)="<<sum_n_k<<endl;
return 0;
}
int sum(int m)
{
int i,sum_m=1;
for(i=1;i<=m;i++)
sum_m*=i;
return sum_m;
}
//以递归的方式算C(n,k)
#include <iostream>
using namespace std;
int sum(int n,int k);
int main()
{
int n,k;
cout<<"请输入C(n,k)中的n值："<<endl;
cin>>n;
cout<<"请输入C(n,k)中的k值："<<endl;
cin>>k;
if(n<k)
{
cout<<"error,please input again."<<endl;
return 0;
}
cout<<"C(n,k)="<<sum(n,k)<<endl;
return 0;
}
int sum(int n,int k)
{
	if(k>n/2)
		k=n-k;
	if(k==0||n==1)
		return 1;
     else return sum(n-1,k)+sum(n-1,k-1);
}