9.6.4. Beyond for Loops // Input Validation // while loops

const input = require('readline-sync');

let num = input.question('Please enter a positive number:');
num = Number(num);

while (num <= 0) {
   num = input.question('Invalid input. Please enter a positive number:');
   num = Number(num);
}

/*This program is an example of input validation. It prompts the user to 
enter a positive number, converting the input string to the number data
type. If the number is not positive, then the user is prompted again 
within the body of the loop. As long as the user continues to input 
non-positive numbers, the loop will continue to iterate.

This example illustrates the additional flexibility provided by while 
loops. While we use for loops to iterate over fixed collections 
(a string, an array, a collection of integers), the while loop can 
be used to iterate in more general circumstances. For the input 
validation example, at runtime it cannot be determined how many times
the loop will repeat.*/