C++ Beginner Issue with moving b/w Functions - c++

Question

This is my first stackoverflow post, so apologies if it's poorly written or the like, but I am a super-beginner at C++ (As will likely be evident in the code) and am trying to complete the 100 Programming Challenge, I am only up to #3 - Temperature Converter.
My friend who has some programming experience in other languages is going to flick through it on my github tonight and see if he can't figure it out, but I thought I'd try stackoverflow as well.
I have no idea what specifically is causing the error so I'm going to have to post the entire code, but basically my issue is that it compiles fine, but when any input is entered it triggers cin.fail() and just loops around and jumps between functions almost seeming of it's own accord, however never entering CelstoFahr() or FahrtoCels().
Apologies again if my code is messy, if you have any suggestions please let me know, and feel free to critique my style as I'm always looking to improve. I can also link my github if necessary.
Code below:
#include "stdafx.h"
#include <iostream>
#include <string>
#include <limits>
// Forward declaring the functions
double CinFailCheck(double cin_fail_check);
double CelstoFahr(double celsius_amount, double fahrenheit_amount);
double FahrtoCels(double celsius_amount, double fahrenheit_amount);
int UserSelectionValidate(int user_selection);
void pauseAtEnd();
bool UserRestart();
void menu();
// Initializing the functions, with user input validation, for Cels -> Fahr, Fahr -> Cels and User Selection
double CinFailCheck(double cin_fail_check)
{
while (std::cin.fail())
{
std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
std::cout << "\nBad entry, no text allowed! Enter a Number: ";
std::cin >> cin_fail_check;
}
return cin_fail_check;
}
double CelstoFahr(double celsius_amount, double fahrenheit_amount)
{
// Declaring cin_fail_check to enable me to have the cin.fail() as a function
double cin_fail_check = 0;
// Perform cin.fail() on the users input then grab that input and clone it to celsius_amount
CinFailCheck(cin_fail_check);
celsius_amount = cin_fail_check;
std::cin.clear();
std::cin.ignore();
// Make conversion using the formula for C to F
fahrenheit_amount = (celsius_amount * 1.8) + 32;
return fahrenheit_amount;
}
double FahrtoCels(double celsius_amount, double fahrenheit_amount)
{
// Declaring cin_fail_check to enable me to have the cin.fail() as a function
double cin_fail_check = 0;
// Perform cin.fail() on the users input then grab that input and clone it to fahrenheit_amount
CinFailCheck(cin_fail_check);
fahrenheit_amount = cin_fail_check;
std::cin.clear();
std::cin.ignore();
// Make conversion using the formula for F to C
celsius_amount = (fahrenheit_amount - 32) * (5 / 9);
return celsius_amount;
}
int UserSelectionValidate(int user_selection)
{
// Declaring cin_fail_check to enable me to have the cin.fail() as a function
double cin_fail_check = 0;
// Perform cin.fail() on the users input then grab that input and clone it to user_selection
CinFailCheck(cin_fail_check);
user_selection = cin_fail_check;
std::cin.clear();
std::cin.ignore();
return user_selection;
}
// Function to enable a pause at the end to avoid the use of system("pause")
void pauseAtEnd()
{
std::cout << "\n\nPlease press Enter to exit . . .";
std::cin.sync();
std::cin.get();
}
// Restart function to avoid having to re-write it all each time
bool UserRestart()
{
bool CONVERTER_RUNNING = true;
bool BOOL_RETURNTOMENU = true;
std::string user_returntomenu;
// Check if the player wishes to make another conversion or exit the program
while (BOOL_RETURNTOMENU == true)
{
std::cout << "\nDo you wish to make another conversion? Y/N: ";
std::cin >> user_returntomenu;
std::cin.ignore();
if (user_returntomenu == "Y" || user_returntomenu == "y" || user_returntomenu == "N" || user_returntomenu == "n")
{
if (user_returntomenu == "Y" || user_returntomenu == "y")
{
std::cin.clear();
std::cin.ignore();
menu();
}
else
{
std::cout << "\nGoodbye";
BOOL_RETURNTOMENU = false;
}
}
else
{
std::cout << "\nBad Entry! Numbers not allowed! Please enter Y or N\n";
std::cin.clear();
std::cin.ignore();
}
}
CONVERTER_RUNNING = false;
return CONVERTER_RUNNING;
}
// Writing the menu() function to enable loopback from the restart function
void menu()
{
int user_selection = 0;
double celsius_amount = 0;
double fahrenheit_amount = 0;
std::cout << "Welcome to the Temperature Converter!\n\n";
std::cout << "1. Convert Celsius to Fahrenheit\n";
std::cout << "2. Convert Fahrenheit to Celsius\n";
std::cout << "3. Exit program\n";
UserSelectionValidate(user_selection);
if (user_selection == 1)
{
// Run Celsius to Fahrenheit function and retrieve the values to cout here
CelstoFahr(celsius_amount, fahrenheit_amount);
// cout the amounts received from the function
std::cout << "\n" << celsius_amount << " degrees Celsius is equal to " << fahrenheit_amount << " degrees Fahrenheit";
}
else if (user_selection == 2)
{
// Run Fahrenheit to Celsius function and retrieve the values to cout here
FahrtoCels(celsius_amount, fahrenheit_amount);
// cout the amounts received from the function
std::cout << "\n" << fahrenheit_amount << " degrees Fahrenheit is equal to " << celsius_amount << " degrees Celsius";
}
else if (user_selection == 3)
{
std::cout << "\nGoodbye";
}
else
{
std::cin.clear();
std::cin.ignore();
std::cout << "\nPlease enter a number between 1 and 3 for your selection!\n\n";
UserSelectionValidate(user_selection);
}
}
int main()
{
// Declare boolean variable to keep converter running
bool CONVERTER_RUNNING = true;
while (CONVERTER_RUNNING == true)
{
menu();
UserRestart();
}
pauseAtEnd();
return 0;
}

Answer 1

Here is one issue:
UserSelectionValidate(user_selection);
This can't have an effect on user_selection, since it is passed by value, and the return value isn't used. Perhaps you meant
user_selection = UserSelectionValidate();
And just have the user_selection declared locally in UserSelectionValidate:
int UserSelectionValidate()
{
// Declaring cin_fail_check to enable me to have the cin.fail() as a function
double cin_fail_check = 0;
// Perform cin.fail() on the users input then grab that input and clone it to user_selection
CinFailCheck(cin_fail_check);
int user_selection = cin_fail_check;
std::cin.clear();
std::cin.ignore();
return user_selection;
}
There is a similar issue with CinFailCheck().

Answer 2

You need to write correct code to store the input user_selection.
std::cout << "Welcome to the Temperature Converter!\n\n";
std::cout << "1. Convert Celsius to Fahrenheit\n";
std::cout << "2. Convert Fahrenheit to Celsius\n";
std::cout << "3. Exit program\n";
UserSelectionValidate(user_selection);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Replace above line with:
std::cin >> user_selection;
Then make sure that you ask for input values to be converted. You can do this.

Answer 3

You need to understand pass by value, and pass by reference. In almost all your functions you are passing by value and not using the return value. When you pass by value, a local variable is created (on the stack) by copying the one passed to it. When you modify it, you are not modifying the original variable passed.
For instance, in the code below, cin_fail_check never changes, it will always have the initialization value of 0, because CinFailCheck does not modify it; you can see how you would get endless loops from this.
// Declaring cin_fail_check to enable me to have the cin.fail() as a function
double cin_fail_check = 0;
// Perform cin.fail() on the users input then grab that input and clone it to user_selection
CinFailCheck(cin_fail_check);
int user_selection = cin_fail_check;
Change your function definitions to take references. For instance: double CinFailCheck(double& cin_fail_check) or use the return value.
"When to pass parameters by value, reference, and pointer"
http://www.cplusplus.com/articles/z6vU7k9E/