Validate input data in an array C++

Question

I have this program that i took it out from: https://intcpp.tech-academy.co.uk/input-validation/ and it works fine, i did some changes because i need the program to keep asking the user to enter a valid input, so that why it has the while in there however it only asks 4 times after that 4th time the input will be valid it does not matter if it right or not, Does any one know how i can fix this. Thank you

#include <iostream>
#include <string>
#include <cctype>

using namespace std;

int main () {

    cout << "Please enter name:" << endl;
    string userName;
    getline(cin, userName);

    bool rejected = false;

    while (rejected == false)
    {
        for (unsigned int i = 0; i < userName.length() && !rejected; i++)
        {

            if (isalpha(userName[i]))
                continue;

            else if (userName[i] == ' ')
                continue;

            else
            {
                cout << "Error, Please enter Patient's name again, First Name: ";
                getline(cin, userName);
                rejected = false;
            }

        }
        rejected = true;
    }

    system("pause");
    return 0;
}

May I suggest you do some rubber duck debugging on your code? Or use an actual debugger to step through the code line by line? That should help you figure out the error pretty quickly. — Some programmer dude
– Some programmer dude, Commented Nov 15, 2018 at 2:11
i think i found the program, break works fine too and the way you show me too but rejected = true; where should be that on at? i tried in 3 different places and in one seems to do nothing until you add a letter in the 2 to places seems to run only one time. Thank you — Rosario Monroy
– Rosario Monroy, Commented Nov 15, 2018 at 3:07

Some programmer dude · Accepted Answer · 2018-11-15 03:09:05Z

1

Personally I would do something like

bool is_valid_username(std::string const& username)
{
    // First trim the string of all leading and trailing white-space
    trim(username);

    if (username.length() == 0)
        return false;  // Input was empty or all spaces

    return std::all_of(begin(username), end(username), [](char const ch)
    {
        return std::isalpha(ch) || ch == ' '; // Only letters and spaces are allowed
    });
}

std::string get_username()
{
    std::string username;

    do
    {
        std::cout << "Please enter username: ";
        std::getline(std::cin, username);
    } while (!is_valid_username(username));

    return username;
}

_{[For the trim function please see this old answer]}

The get_username function will continue to ask for a username forever if the input is either empty, all spaces, or contains non-letters or not a space.

Here's a reference for std::all_of.

Here's a reference about lambda expressions.

edited Nov 15, 2018 at 3:09

answered Nov 15, 2018 at 2:56

Some programmer dude

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4 Comments

Rosario Monroy Over a year ago

thank you, this one is seems to be working fine but the part i posted it only a part of my program, i dont know how i can join this way to the other part of my program. Thank you so much.

Some programmer dude Over a year ago

@RosarioMonroy All the code to read and verify the name in your question could be removed and replaced with a single line string userName = get_username();.

Some programmer dude Over a year ago

@RosarioMonroy Also note that while the use of trim(username) is good to have, it's optional.

Rosario Monroy Over a year ago

How do i call it from main?

Lê Tuấn Anh · Accepted Answer · 2018-11-16 09:39:35Z

0

    if (isalpha(userName[i]) || (userName[i] == ' '))
        continue;
    else
    {
        cout << "Error, Please enter Patient's name again, First Name: ";
        getline(cin, userName);
        i = -1; //Reset check name
    }

Try it! Change unsigned int to int

edited Nov 16, 2018 at 9:39

answered Nov 15, 2018 at 2:38

Lê Tuấn Anh

11 bronze badge

2 Comments

Tas Over a year ago

Resetting i to 0 won't work, because it will be incremented in the next loop so it will check from 1, so if the first character was an invalid one this would still pass.

Tas Over a year ago

You definitely don't want to -1 because it's an unsigned int, so it will break immediately from the for loop

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