Find length of the largest region in Boolean Matrix

#include<bits/stdc++.h>
using namespace std;

//map<int,vector<int> >adj;
//map<int,bool>visited;

int n,m;
 bool visited[100][100];

int a[100][100];

bool is_safe(int i,int j)
{
    return (i>=0 && i<n && j<m && j>=0 && a[i][j] && !visited[i][j]);
}





void dfs(int i,int j,int &countr)
{
   int row[8] = {-1,-1,-1,0,0,1,1,1};
   int col[8] = {-1,0,1,-1,1,-1,0,1};

   visited[i][j] = true;

   for(int k=0;k<8;k++)
   {
       if(is_safe(i+row[k],j+col[k]))
       {   countr++;
           dfs(i+row[k],j+col[k],countr);
       }
   }

}




int main()
{
    cin>>n>>m;

   for(int i=0;i<n;i++)
   {
       for(int j=0;j<m;j++)
       {
           cin>>a[i][j];
       }
   }


   memset(visited,0,sizeof(visited));
   int largest_region=0,count_region=0;

   for(int i=0;i<n;i++)
   {
       for(int j=0;j<m;j++)
       {  int counting=1;
           if( a[i][j] && visited[i][j]==0)
             {
                 count_region++;
                 dfs(i,j,largest_region);

             }

             largest_region=max(largest_region,counting);
       }
   }

   cout<<"No_of_regions : "<<count_region<<endl;
   cout<<"maximum nodes in a region : "<<largest_region<<endl;




    return 0;
}