I'm trying to print all even numbers from 10 to 40 using just a while loop in Javascript. But when I execute the code in the Chrome Browser console I only see 10. Here is my code:

var x = 10;

while (x !== 41 && x % 2 == 0){
  console.log(x)
  x++
}

I'm trying to print all even numbers from 10 to 40 using just a while loop in Javascript. But when I execute the code in the Chrome Browser console I only see 10. Here is my code:

var x = 10;

while (x !== 41 && x % 2 == 0){
  console.log(x)
  x++
}

• javascript
• while-loop

• 1 The loop stops as soon as x % 2 == 0 is false, before you reach the point when x !== 41 is false. – VLAZ Commented Oct 7, 2019 at 11:50
• Just a quick note on while loops, conditions that break on strict equality are not the best. x !== 41 would be better done as x < 41. – Keith Commented Oct 7, 2019 at 11:55

4 Answers 4

The problem is the x % 2 == 0 part. As soon as x bees 11 the loop exits, because that condition evaluates to false. For the loop to continue, both conditions inside the while() parantheses have to evaluate to true as you are using the && operator.

You should move that specific condition to an if statement inside the loop, like so:

var x = 10;
while (x !== 41) {
  if (x % 2 == 0)
    console.log(x);
  x++;
}

The solution above keeps going until x is 41 in which case it will exit the loop and only runs the console.log(x) statement, if x % 2 is equal to 0 (x is even).

A tip I would like to give you is to make a habit of using === instead of ==. This will ensure your value is of the correct type (e.g. x == 2 is true when x is "2" but x === 2 will return false as the type is different) and might help you catch a few errors when debugging.

Another tip would be to use x < 41 instead of x !== 41, it's more monly used and it is easier to read through for most people.

As you are incrementing x by one, at first iteration the value of x bees 11(odd) and the while condition is breaking. You can increment x by 2 as below.

var x = 10;
while (x <= 40){
    console.log(x);
    x += 2;
}

x = 10;
while(x < 41) {
  if(x % 2 == 0) {
    console.log(x);
  }
  x++;
}

As you increase the i one by one, the value of the i bees 11 (odd) on the first iteration, while the level breaks. Can be increased by i 2 as shown below.

   i = 10
        while (i < 40) {
            i += 2;
            document.write("<br>",i);
            console.log(i)
        }