#0: 100% RE (SIGFPE)

溢位或者除以0的錯誤!! 
Floating point exception (core dumped)

#include
using namespace std;
unsigned long long int gcd(unsigned long long int a,unsigned long long int b){
	if(b==0)	return a;
	else	gcd(b,a%b);
}
int main(){
	unsigned long long int N , M ;
	while(cin>>N>>M){
		int rM=M;
		if(N==M and N==0) break;
		if(M>=N/2){
			M = N-M;
		}
		unsigned long long int a=1 ,i,tmp,g,g2;
		for(i=1;i<=M;i++){
			tmp = i;
			g = gcd(a,tmp);
			g2 = gcd((N-i+1),tmp);
			if(g!=1 and g2!=1){
				a = (a/g) * ((N-i+1)/g2) / (i/g/g2);
			}
			else if(g!=1){
				a = (a/g) * (N-i+1) / (i/g);
			}
			else if(g2!=1){
				a = a * ((N-i+1)/g2) / (i/g2);
			}
			else	a = a * (N-i+1) / i;
		//	cout << "a= " << a << " (N-i+1)= " << N-i+1 << " i= " << i << " g= " << g << " g2= " << g2 <<endl;
		}
		cout << N << " things taken " << rM << " at a time is " << a << " exactly."<< endl;
	}
}

 

更新 通過了

//UVA 00369 Combinations

#include<iostream>

using namespace std;

unsigned long long int gcd(unsigned long long int a,unsigned long long int b){

if(b==0) return a;

else gcd(b,a%b);

}

int main(){

unsigned long long int N , M ;

while(cin>>N>>M){

int rM=M;

if(N==M and N==0) break;

if(M>=N/2){

M = N-M;

}

unsigned long long int a=1 ,i,tmp,g,g2;

for(i=1;i<=M;i++){

tmp = i;

g = gcd(a,tmp);

g2 = gcd((N-i+1),tmp);

// cout << "a= " << a << " (N-i+1)= " << N-i+1 << " i= " << i << " g= " << g << " g2= " << g2 <<endl;

if(g!=1 and g2!=1 and i>=g*g2){

a = (a/g) * ((N-i+1)/g2) / (i/g/g2);

}

else if(g!=1){

a = (a/g) * (N-i+1) / (i/g);

}

else if(g2!=1){

a = a * ((N-i+1)/g2) / (i/g2);

}

else a = a * (N-i+1) / i;

// cout << "a= " << a << " (N-i+1)= " << N-i+1 << " i= " << i << " g= " << g << " g2= " << g2 <<endl;

}

cout << N << " things taken " << rM << " at a time is " << a << " exactly."<< endl;

}

}