Ma trận kề trong lý thuyết đồ thị

mọi người cho mình hỏi cái hàm bool ktradothihoplehay_ko(string s) sao nó bị lỗi hoài vậy

#include <iostream>
#include <fstream>
#define max 100
using namespace std;
int n;
int a[max][max];
void ghifile(string s);
void docfile(string s);
bool ktradothihoplehay_ko(string s);
int main()
{

	int chon=1;
	string s="E:\dl.txt";
	while (chon!=0)
	{
	    cout<<"    menu      "<<endl;
		cout<<" 1. ghi file vao tep "<<endl;
		cout<<" 2. doc  file"<<endl;
		cout<<" 3.kiem tra do thi co hop le ko"<<endl;
		cout<<" 0. thoat"<<endl;
		cout<<" bam chon";
		cin>>chon;
		if(chon==1)ghifile(s);
		if(chon==2) docfile(s);
		if(chon==3)ktradothihoplehay_ko(s);
	}
}
void ghifile(string s)
{
	int n, a[max][max];
  ofstream matran (s,ios :: out) ;
  cin>>n;
  matran<<n<<endl;
  
  for(int i=0;i<n;i++)
  {
   for(int j=0;j<n;j++)
     {
         cin>>a[i][j];  
         matran<<a[i][j]<<"  ";      
     }        
     matran<<"
";
  }
  matran.close();
}
void docfile(string s)
{
int n, a[max][max];
    ifstream nhuy (s,ios :: in);
    if(nhuy.fail()){
        cout << "Kiem tra lai file dau vao!";
        system("pause");
    }
  
    nhuy >> n;
    for (int i = 0; i < n; i ++)
    {
        for (int j = 0; j < n; j ++)
        {
            nhuy>> a[i][j];
            cout << a[i][j] << " ";
        }
        cout << endl;
    }
    nhuy.close();
}

bool ktradothihoplehay_ko(string s)

{

	for(int i=0;i<n;i++)
		if(a[i][i]!=0)
			return 1;
		else
			return 0;
}