Find k’th character of decrypted string

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

int main() {
	
	int t; cin>>t;
	
	while(t--)
	{
	    string s; int k; cin>>s>>k; int i=0,n=s.length();
	    
	    string main_string("");
	    
	    while(i<n)
	    { string local_string="";
	       while(i<n && isalpha(s[i]))
	       {
	           local_string+=s[i];
	           i++;
	       }
	       
	       string num="";
	       
	       while(i<n && isdigit(s[i]))
	       {
	           num+=s[i];
	           i++;
	       }
	       
	       int freq=atoi(num.c_str());
	       
	       for(int p=1;p<=freq;p++)
	         main_string+=local_string;
	       
	    }
	    
	    cout<<main_string[k-1]<<endl;
	}
	

	return 0;
}