closing while(cin.good()) loop properly

Question

I'm trying to make the program exit properly without it. I have '|' as my exit, if its the first thing I do when first running, it closes fine. But after entering values and printing them, afterwards entering '|' to exit. It prints out: "The smaller value is 0 The larger is previous second value" // want to remove this from showing

int main()
{    
double first = 0, second = 0;
while(cin.good()){
    char exit;
    cout << "Enter '|' to exit.\n";
    cout << "Enter two numbers:";
    cin >> first >> second;
    exit = cin.peek();

    if(exit=='|'){
        break;}
    else{
        if(first<second){
            cout << "\nThe smaller value is " << first << "\nThe larger value is " << second << endl;
        }
        else if(first>second){
            cout << "\nThe smaller value is " << second << "\nThe larger value is " << first << endl;
        }
    }
  }
}

Answer 1

In your code, you've assumed that the input from your users will be limited to something usable as a double. This isn't necessarily the case. The issue that you're running into isn't related to the statement exit = cin.peak(); but to cin >> first >> second; You can test this by entering any non-numerical input into your program and watching it fail by assigning a 0 to the first and leaving second as is.

In short, because the conversion of the input into a double fails, you get an indeterminate value for first and then your program moves on.

You can use the following code as an example. In this, I first populate my variables as strings, then attempt a conversion after the fact.

#include <iostream>
#include <string>
#include <stdlib.h>
using namespace std;

int main()
{    
string str_first, str_second;
double first = 0, second = 0;
while(cin.good()){
    cout << "Enter '|' to exit.\n";
    cout << "Enter two numbers:";
    cin >> str_first >> str_second;

    if( (str_first.compare("|") == 0) || (str_second.compare("|") == 0) ){
        cout << "\nThanks for playing\n" << endl;
    break;}
    else{
        first = strtod (str_first.c_str(), NULL);
        second = strtod (str_second.c_str(), NULL);
        if(first<second){
           cout << "\nFirst is small: The smaller value is " << first << "\nThe larger value is " << second << endl;
        }
        else if(first>second){
            cout << "\nSecond is small: The smaller value is " << second << "\nThe larger value is " << first << endl;
        }
    }
  }
}