Help me in solving STCV203 problem

My issue

how the indices in case 1 is same

My code

// Update the '_' in the code below to solve this problem

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

int main() 
{
  int t;
  cin>>t; 
  while(t--)
  {
   string A,B;
   cin>>A>>B;
   // variable to store the count of '1's in A
   int a_count = 0;
   // variable to store the count of '1's in B
   int b_count = 0;
   // variable to store the count of indices where A[i] = B[i]
   int common = 0;

  // Count '1s' in A
   for(int i=0; i<A.length();i++)
      {
        if(A[i]==__)
          {
            a_count++;
          }
          
      }

  // Count '1s' in B
   for(int i=0; i<B.length();i++)
      {
        if(B[i]==__)
          {
            b_count++;
          }
          
      }
  // Count indices where A[j] = B[j] 
   for(int i=0; i<A.length();i++)
      {
        if(__==__)
          {
            common++;
          }
          
      }
  cout<<a_count<<" "<<b_count<<"  "<<common<<endl;
  }
 return 0;
}
   

Learning course: C++ for problem solving - 2
Problem Link: CodeChef: Practical coding for everyone

@prabhakarpiyus
What with the indexes, I didn’t get your issue .
Its a simple problem u have to count 1’s in A and B and the common index same elements and print them.