john    123
jim 89
britney 852

john  123
jim  89
britney  852
britney  852

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
  string passwd;
  string usern;
  string password;
  string username;
  ifstream infile;
  string line;
  infile.open("sample.txt");
  if(!infile)
  {
    cerr << "error during opening of the file" << endl;
  }
  else
  {
    while (!infile.eof())
    {
      infile >> usern >> passwd ;
      cout << usern << " " << passwd << endl;
    }
  }
  cout << "Enter user name : ";
  cin >> username;
  if (usern == username)
  {
    cout << "already exist" << endl;
  }
  infile.close();
  return 0;
}