How to make a while loop but with more conditions C++

Question

cout << "Options:\n1: Change Name\n2: Change Password\n3: Change Address\n4: Withraw\n5: Deposit\nL: Log out\n>";
while (user_input2 != '1' && user_input2 != '2' && user_input2 != '3' && user_input2 != '4' && user_input2 != '5' && user_input2 != 'L')
{
    cout << "Invalid input";
}

So how do I just shortened the while conditions?

I tried doing:

cout << "Options:\n1: Change Name\n2: Change Password\n3: Change Address\n4: Withraw\n5: Deposit\nL: Log out\n>";
while (user_input2 != '1','2','3','4','5','L')
{
    cout << "Invalid input";
}

but it doesn't work.

edit1: "I added more hints to what I wanted to do"

The comma operator may compile but it will not do what you want. — drescherjm, Nov 29 '20 at 23:44
I think you made a mistake in your first block code. By using "or" `||`, the condition will always be satisfied with any value `user_input` can take. I think you meant to use the "and" `&&` operator. — Patrick, Nov 29 '20 at 23:45
This seems like a dupe https://stackoverflow.com/questions/61447353 though it uses `if` instead of `while`. — cigien, Nov 29 '20 at 23:49
I just found an older duplicate but that one is better. [https://stackoverflow.com/questions/15181579/c-most-efficient-way-to-compare-a-variable-to-multiple-values](https://stackoverflow.com/questions/15181579/c-most-efficient-way-to-compare-a-variable-to-multiple-values) — drescherjm, Nov 29 '20 at 23:51
Are the values that you're comparing against always going to be chars? And will they be contiguous? — cigien, Nov 30 '20 at 00:10
Ok, and will they be contiguous, i.e. do you care about cases like `user_input2 != '1','3','5', '8'`? — cigien, Nov 30 '20 at 02:25
Actually I don't care if the numbers are in order or not, these chars are just options plus the L which will be the quitting option to the while loop, I'm just wondering which is a way where the "user_input2 !=" condition to be implemented to all the chars I want without typing too much. Thank you in advance. :) — MJ DLS, Nov 30 '20 at 05:28

Mureinik · Answer 1 · 2020-11-30T08:26:47.007

9

You can use the < and > operators for the range of '1' to '5', but you'll have to handle the check for 'L' explicitly:

while (user_input2 != 'L' && (user_input2 < '1' || user_input2 > '5'))
{
    cout << "Invalid input";
}

edited Nov 30 '20 at 08:26

answered Nov 29 '20 at 23:38

Mureinik

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1

Maybe a short explanation about character encodings to help a beginner programmer? – Patrick Nov 29 '20 at 23:40
3

@Patrick — character encodings aren’t really involved here. In C++ and C the digits `[‘0’ .. ‘9’]` are required to be contiguous and increasing. So that test is valid for every character encoding that the compiler supports. – Pete Becker Nov 30 '20 at 01:56
it didn't work, the char inputs have an L in it. so the options are ('1','2','3','4','5','L') – MJ DLS Nov 30 '20 at 05:19
@MJDelosSantos A little more effort. The condition proposed here takes care of cases where `user_input2` is a digit between 1 and 5. If you have an extra valid character you can use this: `input < '1' || input > '5' || input == 'L'`. – Patrick Nov 30 '20 at 06:40

deepv2 · Answer 2 · 2020-11-30T00:33:17.137

3

You also can write:

while (user_input2 != '1' && user_input2 != '2' && user_input2 != '3' && user_input2 != 
'4' && user_input2 != '5')
{
    cout << "Invalid input"
}

edited Nov 30 '20 at 00:33

answered Nov 29 '20 at 23:40

deepv2

51
10

This while conditions are just too long, I just want to shortened it to save my fingers and time typing it. – MJ DLS Nov 30 '20 at 02:07

Scheff's Cat · Answer 3 · 2020-11-30T07:35:22.523

How about a function where you provide all accepted characters as string?

Demo:

#include <iostream>

bool checkValid(char cChk, std::string_view allowed)
{
  for (char c : allowed) if (cChk == c) return true;
  return false;
}

int main()
{
  char user_input2;
  std::cin >> user_input2;
  if (!checkValid(user_input2, "12345L")) {
    std::cout << "Invalid input\n";
  }
}

Live Demo on coliru

Btw. there is a standard C library function (adopted in C++ standard) which could be used as well:

std::strchr()

It returns a pointer to found character or nullptr and could be used similar like checkValid() in the above sample:

#include <cstring>
#include <iostream>

int main()
{
  char user_input2;
  std::cin >> user_input2;
  if (!std::strchr("12345L", user_input2)) {
    std::cout << "Invalid input\n";
  }
}

Live Demo on coliru

Thinking twice (about OPs possible intention), I started to ask why the check is needed at all. Assuming that the valid input has to be processed somehow (I would use a switch for this), invalid input just could be covered as well.

Demo:

#include <iostream>

int main()
{
  for (char user_input2; std::cin >> user_input2;) {
    switch (user_input2) {
      case '1': std::cout << "Change Name\n"; break;
      case '2': std::cout << "Change Password\n"; break;
      case '3': std::cout << "Change Address\n"; break;
      case '4': std::cout << "Withraw\n"; break;
      case '5': std::cout << "Deposit\n"; break;
      case 'l': case 'L': std::cout << "Log out\n"; return 0;
      default: std::cerr << "Invalid input!\n";
    }
  }
}

Input:

12AL

Output:

Change Name
Change Password
Invalid input!
Log out

Live Demo on coliru

How to make a while loop but with more conditions C++

3 Answers3