做分数的题时都可以用，但是不支持负数

class fractional{
private:
	int a,b;//a/b
	double origin;//小数值 
public:
	int gcd(int x,int y){//返回最大公约数 
		return (y==0)?x:gcd(y,x%y);
	}
	int lcm(int x,int y){//返回最小公倍数 
		return x*y/gcd(x,y);
	}
	void reduct(){//约分 
		int g=gcd(a,b);
		a/=g;b/=g;
	}
	fractional():a(0),b(1),origin(0.00){}
	fractional(int x,int y):a(x),b(y){//初始化 
		if(y<=0||x<0){
			cout<<"It's not a correct fractional!";//分母不能为0,不支持负数 
			y=1;
		}
		origin=(double)1.00*a/b;
		reduct();
	}
	void output(){//输出，可根据题目修改 
		cout<<a<<"/"<<b;
	}
	//关系运算符判断 
	bool operator<(fractional& fr){return this->origin<fr.origin;}
	bool operator<=(fractional& fr){return this->origin<=fr.origin;}
	bool operator>(fractional& fr){return !((*this)<=fr);}
	bool operator>=(fractional& fr){return !((*this)<fr);}
	bool operator==(fractional& fr){return this->origin==fr.origin;}
	bool operator!=(fractional& fr){return !((*this)==fr);}
	
	fractional reciprocal(fractional& fr){//返回一个分数的倒数 
		fractional ans(fr.b,fr.a);
		return ans;
	}
	//四则运算 
	fractional operator+(fractional& fr){
		fractional ans(this->a*fr.b+this->b*fr.a,this->b*fr.b);
		return ans;
	}
	fractional operator*(fractional& fr){
		fractional ans(this->a*fr.a,this->b*fr.b);
		return ans;
	}
	fractional operator-(fractional& fr){
		fractional ans(this->a*fr.b-this->b*fr.a,this->b*fr.b);
		return ans;
	}
	fractional operator/(fractional& fr){
		fractional ans(this->a*fr.b,this->b*fr.a);
		return ans;
	}
};

本题示例：

vector<fractional> v;
int main()
{
	int n;
	cin>>n;
	cout<<"0/1"<<endl;
	for(int i=1;i<=n;i++){
		for(int j=i;j<=n;j++){
			if(gcd(i,j)==1){
				fractional f(i,j);
				v.push_back(f);
			}
		}
	}
	sort(v.begin(),v.end());
	for(int i=0;i<v.size();i++){
		v[i].output();
		cout<<endl;
	}
	return 0;
}