Can anyone explain the following?

Question

var arr=[1,2,3,4];
var ct=4
for(let i=0;i<ct;i++){
ct--;
arr[i]+=i
}
document.write(arr);
Ans: 1,3,3,4

Answer 1

//You got an array
var arr=[1,2,3,4];
//A counter variable named ct
var ct=4
//You run a for loop from 0 as long as i is less than ct
for(let i=0;i<ct;i++){
//we decrement ct each time the loop runs
ct--;
//we increment the array element at position i by the value of i whenever this loop runs
arr[i]+=i
// 1st run of this loop
//arr[0]+=0 //Now i is 1, ct is 3(ct--), original array is unchanged
//2nd run of this loop
//arr[1]+=1 //Now i is 2, ct is 2(ct--) and now we also incremented arr[1] by 1 [1, 2, 3, 5] -> [1, 3, 4, 5]
//loop terminates as i is no longer less than ct
//i = 3, ct=3
}
document.write(arr) //print

Answer 2

For the first value it adds 0
So 1 still is 1
In the second run of the loop ct becomes 2
And i is 1
So to the 2 in the arr it adds 1.
Then i becomes 2 and is no longer smaller than ct and so the loop stops and prints 1 3 3 4

Answer 3

Thanks Lord Krishna

Answer 4

Dragonxiv Thanks but I didn't get, may you please explain it in a gradual manner.