Changing for loop to while loop crashes javascript webpage?

Question

New to JS. I'm trying to change my for loop to a while loop. It prints the factors of a number, but for some reason, the while loops causes the webpage to stop responding. Any help is appreciated.

var num, i = 1,
  array = [];

num = parseInt(prompt("Please enter a number:"));

while (i < num) {
  if (num % i == 0) {
    array.push(i);
    i++;
  }

}
alert("The factors of " + num + " are: " + array + " and " + num);

You might wanna give num a value if the prompt did not return a numeric value or not a value at all, you might end up with NaN which would also fall into the case of i < num returning false — a-d
– a-d, Commented Mar 5, 2017 at 18:42

kind user · Accepted Answer · 2017-03-05 18:36:38Z

4

Move the incrementation of i variable outside the if condition. Else - the while loop will be stuck when the num is not divisible by specified i.

For example - if num is 5 and i is 2, the loop will be stuck because the if condition is not fulfilled - that's why i won't be incremented - and then we will experience an infinite loop.

var num, i = 1, array = [];
num = parseInt(prompt("Please enter a number:"));

while (i < num) { 
   if (num % i == 0) {
      array.push(i);
   }
   i++;
}
alert("The factors of " + num + " are: " + array + " and " + num);

edited Mar 5, 2017 at 18:36

answered Mar 5, 2017 at 18:32

kind user

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1 Comment

icewolf461 Over a year ago

so simple xd. Thank you.

Nina Scholz · Accepted Answer · 2017-03-05 18:44:44Z

0

You increment i only if the condition of the "if" block is true. If that condition evaluates to false, i can't be incremented, and therefore the loop never ends.

if (num % i == 0) {  // <some value except 0> % 1 == 0 -> false
    array.push(i);
    i++;
}

so try:

while (i < num) {
    if (num % i == 0) {
        array.push(i);
    }
    i++; // now i can be incremented regardless of the condition in the "if" block.
}

edited Mar 5, 2017 at 18:44

user5937446

answered Mar 5, 2017 at 18:36

Nina Scholz

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