Thread: cannot sort structure !

i am unable to compile this code..can any 1 help

Code:

#include <cstdio>
#include <cmath>
#include <algorithm>
using namespace std;

struct fraction
{
	int num,den;
	
	fraction(){} 
	fraction(int a,int b) {insert(a,b);}
	
	void insert(int a,int b)
	{
		int g=__gcd(a,b);
		if(g!=0) {a/=g;b/=g;} // reducing to lowest terms !
		if(b<0)  {a=-a;b=-b;} // changing the sign !
		num=a;den=b;
	}
	bool operator <(fraction A)
	{
		return (num*A.den-den*A.num<0);
	}
	bool operator >(fraction A)
	{
		return (num*A.den-den*A.num>0);
	}
	bool operator ==(fraction A)
	{
		return (num*A.den-den*A.num==0);
	}
};

int main()
{
	fraction a[100];
	sort(a,a+100);
	return 0;
}

Thank you !