Boolean will not work with while loop

Question

I'm having some trouble with my while looping breaking its cycle. If I answer the problem correctly the first time, it allows me to proceed through the program. However, if I use an integer it loops false, even if I answer it correctly in the loop it will not exit and save the string value. The thing is, is that I don't want a person entering an integer in this question, so I check the line for any integers.

#include "stdafx.h"
#include "stdio.h"
#include <iostream>
#include <ctime>
#include <string>
#include <time.h>
#include <algorithm>
#include "ThreeWayRace.h"
#include <cctype>
#include <functional>


using namespace std;

void Options()
{

string carColor;
int carNumber;
int s;
cout << "Please type a color in for your car: ";
cin>>carColor;
bool contains_non_alpha
    = std::find_if(carColor.begin(), carColor.end(),
        std::not1(std::ptr_fun((int(*)(int))std::isalpha))) != carColor.end();
while (contains_non_alpha == true)
{

    cout << "Please enter letters only. ";
    cin.clear();
    cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    cin>>carColor;

}

contains_non_alpha is not set inside the loop. It's not going to change just by magic... — John3136
– John3136, Commented Jun 22, 2016 at 2:56
In this case you might want to use std::all_of, simply passing std::isalpha as the predicate. Instead of std::find_if I mean. — Some programmer dude
– Some programmer dude, Commented Jun 22, 2016 at 2:59
You might save yourself even more trouble by having a std::set<std::string> of known colour names, then using colour_names.count(carColur) to decide whether to loop asking for a valid colour name.... — Tony Delroy
– Tony Delroy, Commented Jun 22, 2016 at 4:01

Some programmer dude · Accepted Answer · 2016-06-22 03:05:09Z

2

As told by the comments you don't actually do the check in the loop, which means the value of contains_non_alpha will never change.

The simple solution is to do the check itself as part of the condition of the loop, no need for a temporary variable.

Using the std::all_of function as in my comment you could then do e.g.

while (!std::all_of(std::begin(carColor), std::end(carColor), std::isalpha))
{
    ...
}

You could also use a do while loop like this

void Options()
{
    std::string carColor;

    do
    {
        std::cout << "Please type a color in for your car (letters only): ";
        std::cin >> carColor;
    } while (!std::all_of(...));

    int carNumber;
    // ... rest of code...
}

answered Jun 22, 2016 at 3:05

Some programmer dude

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2 Comments

Nathaniel Petterson Over a year ago

....I feel extremely silly for spending hours, upon hours trying to figure out how to check a string value for characters only..... Thanks a ton Joachim!

Some programmer dude Over a year ago

@NathanielPetterson Everything is easy once you know how it's done. :)

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