Flag Controlled Loop

Video Summary: https://youtu.be/zXQKDa5ZoG8

Using the boolean "true" or "false" is referred to as using boolean flags. Boolean flags are often used for control like if statements or while loops as they are often more readable. Consider the example boolean conditions:

 
1	
2	
3	
4	
5	
6	
7	
8	
9	
10	
11	
12	
13	
14	
15	
16	
#include <iostream>
using namespace std;

int main(){
    bool isTrue = true;

    while(isTrue){
        cout << "isTrue is " << isTrue << endl;
        isTrue = !isTrue;
    }

    while(!isTrue){
        cout << "isTrue is " << isTrue << endl;
        isTrue = !isTrue;
    }
}

Note the following from the example:

You do not need to write "isTrue == true" because booleans already carry the value of true or false, which is what control tests for in the first place
When a boolean variable is true, it will output 1, and when it is false it will output 0
The not operator ! is used to check for false, which is equal to "isTrue == false"
You can also use ! to set a boolean to it's opposite value, like on lines 9 and 14

Exercise

In this exercise, you will create a simple registration form requiring an email, password, and confirm password, and perform some field validation.

Create a loop that will repeat whenever the form input is not valid
Set the flag to true at the top of the loop
Prompt the user for the three fields
Check if the email field contains an '@' symbol. If it doesn't, print an error message and set valid to false
Check if the password is more than 5 characters, and if it isn't print an error message and set valid to false
Check if the confirm password field matches password, and if it isn't print an error message and set valid to false
Print "registration successful" if valid stays true and the loop exits

Solution

/*
Program name: formvalidate.cpp
Author: Devon Blewett
Purpose: This program simulates a registration form.  The user enters an email, password and confirm password.  If the email doesn't have an @ symbol, the password isn't larger than 5 characters, or the confirm password doesn't match, error messages are printed and the loop repeats.

Written for the Open Textbooks program
*/

#include <iostream>
using namespace std;

int main(){
    // flag for the loop
    bool valid = false;
    // fields for the form
    string email;
    string password;
    string confirmPassword;

// while the input is not valid
    while(!valid){
        // assume input will be valid
        valid = true;
        // read the inputs
        cout << "Enter email: " << endl;
        cin>> email;
        cout << "Enter password: " << endl;
        cin >> password;
        cout << "Confirm Password: " << endl;
        cin >> confirmPassword;
        // check if the email contains a @ symbol
        if(email.find("@") == string::npos){
            cout << "Username not valid" << endl;
            valid = false;
        }
        // check if the password is long enough
        if(password.length() < 5){
            cout << "Password too short" << endl;
            valid = false;
        }
        // check if the password matches confirmPassword
        if(password != confirmPassword){
            cout << "passwords don't match" << endl;
            valid = false;
        }
    }
    // if valid stayed true, exits to here
    cout << "Registration Successful" << endl;
}

Colour Theme		Font Size Options