About infinite loop(in C++)

Question

It is a part of whole codes. when i try to execute, it operate normally until "Enter month and payment received". However after this message, i put Hash index and value such that "July 315.14". Suddenly, it print "Another query(Y/N)?" in infinite loop. Where is my error point?

          unordered_map<string,float> monthly_payment;
          char query;
          string month;
          cout << "Enter number of payments : ";
          cin >> payNum;
          cout <<"Enter month and payment received : " << endl;
          for(int i=0; i<payNum; i++){
              getline(cin, month,'\n');
              cin >> payment;
              monthly_payment.insert(pair<string, float>(month,payment));
          }
          cout << "Enter query month : ";
          getline(cin, month, '\n');
          cout << "The payment is " << monthly_payment[month]<<endl;
          do{
              cout << "Another query (Y/N)? ";
              cin >> query;
              if(query=='Y'){
                  cout << "Enter query month : ";
                  getline(cin, month, '\n');
                  cout << "The payment is " << monthly_payment[month]<<endl;
              }
          }while(query!='N');

Answer 1

When you have

int i;
string str;
cin >> i;          // [1]
getline(cin, str); // [2]

It stops within [1] and waiting for user input. Then user typed 32 and nothing happened. Then user hits <enter> and input buffer flushes to process 32\n. Program parsed 32 at line [1] and goes to line [2]. It's \n remains to parse so str becomes empty string and program moves forward.

On linux you can make input buffer flash another way. Pressing Ctrl+D for example. So you program becomes usable.

The best way to solve your problem just have

string month;
double payment;
cin >> month >> payment;

Or as alternative you can use geline everywhere and parse string by the hands.