Loop without the use of while loop

Question

2.50/5 (2 votes)

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Hi all, I was wondering for the following, is it possible to keep prompting user input (output window will not be close) without the use of while loops?

In case if I am not clear/ my english is no good, suppose if the user inputs in 20, it will return the output 'Wrong!' but it will re-prompts the user to re-enter in a new number

Can that be done?

C++

#include <iostream>
using namespace std;

bool numCheck (int num);

int main(){
    int input;
    cout << "Enter in a number : ";
    cin >> input;
    
    if (numCheck(input)){
        cout << "Correct!" << endl;
    }
    else{
        cout << "Wrong!" << endl;
    }
}

bool numCheck (int num){
    if (num == 10){
        return true;
    }
    else{
        return false;
    }
}

What I have tried:

I know that using of while loop could possible be the ideal solution for it, but would like to know if there are any other alternatives for something as simple as the code I have posted..

Posted 24-Feb-16 16:55pm

yann00n

Updated 26-Feb-16 13:50pm

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Comments

[no name] 24-Feb-16 23:07pm

As a beginner why look for something else if you know a while loop will work? Every solution will involve some kind of looping. Just use Google - something like "c++ prompt for input loop".

yann00n 24-Feb-16 23:37pm

I did and I have been getting results where while loops are being used... And hence my question

[no name] 24-Feb-16 23:51pm

??

Sergey Alexandrovich Kryukov 25-Feb-16 0:25am

???

Jochen Arndt 25-Feb-16 2:59am

Using a while loop is common for this task. So why use something else?

However, you may use a for loop too as an alternative but it would be more obfuscated.

yann00n 25-Feb-16 21:34pm

I am simply trying to see if there are alternatives ways for while loops.

Arthur V. Ratz 20-Mar-16 11:33am

If you don't need loop while don't you use goto operator instead. But it's poor programming techniques.

4 solutions

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Peter Leow · Answer 1 · 2016-02-24T17:44:00

Solution 1

Based on your requirement, you should use do while[^] instead of while as you have to allow a user to enter at least once before checking the condition.

Posted 24-Feb-16 17:44pm

Peter Leow

Updated 24-Feb-16 17:45pm

v2

Comments

yann00n 25-Feb-16 2:41am

So I suppose only with the use of while or do..while loops, these two are the only ones that enables the output console/window to be present until the user input in the correct value?

Peter Leow 25-Feb-16 3:56am

do...while loop is the right choice.

Richard MacCutchan · Answer 2 · 2016-02-24T22:27:00

Solution 2

See Iteration Statements (C++)[^].

Posted 24-Feb-16 22:27pm

Richard MacCutchan

Patrice T · Answer 3 · 2016-02-26T13:50:00

Solution 4

Quote:
Loop without the use of while loop

It is possible, but there is no point doing so.
There is many fashions to do loops in C but all fall in pretty much the same result, same capacities, same efficiency.
So there is no reason to avoid 1 kind of loop.

Posted 26-Feb-16 13:50pm

Patrice T

Matt T Heffron · Answer 4 · 2016-02-26T13:13:00

As many have said, this problem is clearly best solved wit a loop.
However...as an intellectual exercise:
Yes, you could do it with recursion: Recursion - Wikipedia, the free encyclopedia[^]

C++

#include <iostream>
using namespace std;

bool numCheck(int num);
typedef bool(*CheckFn)(int);
int enterCorrectNumber(CheckFn);

int main(){
  enterCorrectNumber(&numCheck);
}

bool numCheck(int num){
  return (num == 10);
}

int enterCorrectNumber(CheckFn checker){
  int input;
  cout << "Enter in a number : ";
  cin >> input;

  if (checker(input)){
    cout << "Correct!" << endl;
    return input;
  }
	
  cout << "Wrong!" << endl;
  return enterCorrectNumber(checker);
}

You must be careful to use this only when you can bound the number of times the function can call itself or else a stack overflow will occur!
This example is structured in a way called tail-recursion so an optimizing compiler can generate the code in such a way as to prevent the stack overflow from ever happening.