Why do I get 55 when I console this code?

Hello I’m just trying to understand why Im getting 55 as the result from this code Im new lerning while loops, thanks guys

var sum =  0;
var num = 0;
   while (num <= 10) {
   sum += num;
   num++;
}
console.log(sum);
var sum =  0;
var num = 0;
   while (num <= 10) {
   sum += num;
   num++;
}
console.log(sum);

Here in this code the value of num is updating everytime from 1 to 10.
If you try calculating the loop sum= 0 but num = 1+2+4+5+6+7+8+9+10, you will be getting 55.
To understand it much better try changing the value of this

while (num <= 10) 

to

while (num <= 4) 

You’ll get 10, as the value of num gets added.
It works like this

0(sum) = 0 + 1 + 2+ 3+ 4;

2 Likes

Hi,
Initially, the value of sum and num is 0.

For every iterations, there’re 2 things happens:

  • num is added to sum ( sum += num means sum = sum + num )
  • num increased its value by 1 ( num++ means num = num + 1 )

The value of num goes from 0 to 1, to 2, to 3 … to 10 then stops.
So sum = 0 + 1 + 2 + 3 + ... + 10 = 55.

55 is the last value of sum after the loop ended.

3 Likes

2 Likes

thanks lot this concept its much more clear now

thank you very much toan

thanks for your help very useful