C ++ Fraction类不适用于底片

Question

我正在尝试创建一个可以对分数进行操作的分数类，就像我们在小学时手工操作一样。它与正数一起正常工作，但我尝试用负数实现它，我得到断点错误。如果有人能告诉我它有什么问题，那就太好了。

#include <iostream>
#include <cmath>
using namespace std;

class fraction
{
private:
    long int n;
    long int d;
    long int gcd();
public:
    fraction(long int, long int);
    long int num(); //returns num
    long int denom(); //returns denom
    void print(); //print fraction
    void reduce(); //reduce fraction to lowest terms
friend double convert(fraction); //convert function to double
friend fraction operator+ (fraction, fraction);//add two fractions, answer in reduced form
friend fraction operator- (fraction, fraction);//subtract two fractions, reduced
};

long int fraction::gcd()
{
    long int divisor = 0;
    for (long int i = 1; (i <= n && i <= d) ; i++)
    {
        if ((n % i == 0) && (d % i == 0))
        {
            divisor=i;
        }
    }
    return divisor;
}
fraction::fraction(long int x, long int y) //constructor
{
    n=x;
    d=y;
    if ((x <= 0) && (y <= 0))
    {
        n = -x;
        d = -y;
    }
}
void fraction::reduce() //change value of n and d
{
    long int num = n/gcd();
    long int denom = d/gcd();
    n = num;
    d = denom;
}
long int fraction::num()
{
    return n;
}
long int fraction::denom()
{
    return d;
}
void fraction::print() 
{
    cout << n << "/" << d;
}
fraction operator- (fraction x, fraction y) 
{
    x.reduce();
    y.reduce();
    fraction temp;
    temp.n = (x.n)*(y.d) - y.n*(x.d);
    temp.d = (x.d)*(y.d); 
    temp.reduce();
    return temp;
}
int main()
{
    fraction f(-5,100), g(-1,-2);
    (f-g).print; //returns error!
    return 0;
}