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Ask for a value again if user does not enter anything

I have created the mortgage calculatir below. Everything works fine, except if the user does not enter a value and hits enter, my while statement does not catch it. How can I code so that if the user does not enter a value, I ask for it again as it works if they enter a 0.


/*  This program will accept the loan amount, The term of the loan, and the
interest rate and display the monthly payment to the screen. The user
will then be offered the choice of running another loan or quitting.
@author Jon Schab
@version 2.0
Changes for this version - Program altered to accept loan terms rather
than having them hard coded as in the previous version.      

//#include <iostream>
#include <cmath>
#include <iostream>
#include <stdio.h>
#include <conio.h>
#include <ctype.h>
#include <stdlib.h>
#include <math.h>

using namespace std;

int main()

  //declare variables

  double loanAmount; // loan amount
  double interestRate; // interest rate
  double interestRateMonthly; // monthly interest rate
  int termYears; // term of loan in years
  int termMonths; // term in months
  double monthlyPayment; // monthly payment
  char again = 'N'; // NOT char again = Y;

  // Loop to allow the user another calculation      
        // reset fields for anpother mortgage
            loanAmount = 0.00;
            termYears = 0;
            interestRate = 0.00;

    //display questions and recieve input from user.
      cout << endl; // add blank line before title.
    cout << "\t\t\tJon's Mortgage Calculator" << endl << endl; // Calculator Title
      while(loanAmount <= 0.00) //check for positive value
      cout << "\n\n \t\t\t Loan amount: $"; // ask user for loan amount
      cin >> loanAmount;


      while(termYears <= 0) //check for positive value
    cout << "\n      \n \t\t\t Loan Term In Years: "; // ask user for loan term
    cin >> termYears; // capture loan term
      while(interestRate <= 0) //check for positive value
      cout << "\n\n \t\t\t Yearly Interest Rate: "; // ask user for interest rate
    cin >> interestRate; // capture interest rate

    //calculate term in years and monthly interest rate
    interestRateMonthly = ((interestRate / 12) / 100);
    termMonths = (termYears *12);

    //calculate mothly payment
    monthlyPayment = (loanAmount *interestRateMonthly) / (1 - pow(1.0 / (1.0 +
      interestRateMonthly), termMonths));

    //display terms and monthly payment to the screen.
    cout << "\n\n \t\t\t Monthly Payment $" << monthlyPayment << endl << endl;

    // Offer the user another calculation
    cout << (
      "\n\n\t Enter Y or y to calculate another mortgage, any other key to quit  ");
    again = _getch(); // capture response for another calculation                                          
    system("cls"); // clear the screen
  while (again == 'Y' || again == 'y'); // End of loop for another go.

  return 0;
1 Solution
This is really a cin issue.  Used in this form
      cin >> loanAmount;
cin will not return until the user enters a value.  I'm not aware of any simple way to change this behavior.

The best simple solution I'm aware of is something like this
where buffer might be
      char buffer[256];


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