The following outputs 11, 704 and 124 but I can't wrap my head around the reason for their output. Please help a brother..

Question

function addBinary(a,b) {
var sum=a+b;
var res=””;
while(sum>0) {
res=sum%2+res;
sum=Math.floor(sum/ 2);
}
}
alert(addBinary(1,2)); //11

var input=407;
var res=0;
for(i=input;i>0;i=Math.floor(i/10)) {
res=res*10+i%10;
}
document.write(res); //704

var arr=[1];
for(var i=1; i<3; i++) {
arr[i] = arr[i-1]+i;
}
alert(arr.join(“”)); //124

Answer 1

I'm trying to explain third program.
var arr = [1]; // arr[0] = 1;
The loop start with i = 1 and arr[i] = arr[i-1] + 1 is
arr[1] = arr[1-1] + 1 = 1+1=2
Next step i = 2.
arr[i] = arr[i-1] + 1 is
arr[1] = arr[2-1] + 1 = 2+2=4.

Answer 2

Look inside the loop you have arr [i] = arr [i-1] + i. So arr [i-1] is 1 and plus i.

Answer 3

You probably wanted to write i > 0, since that actually makes sense
i in the loop starts as 407. res is 0, so res * 10 + i % 10 is 7. Then, at the end of the iteration, i becomes Math.floor(i / 10), which is 40. res * 10 + i % 10 is 70, since 7 * 10 (70) + 40 % 10 (0) is 70. Then, again, i becomes i / 10 (4). res * 10 + i % 10 = 70 * 10 (700) + i % 10 (4) = 704. 4 divided by 10 is 0(.4), so the loop stops executing.

(it gets reversed)

Answer 4

arr[0] = 1
arr[1] = arr[0] + 1 -> 2
arr[2] = arr[1] + 2 -> 4

Answer 5

Ahmadjon Boboev, why are we adding 1+1 and 2+2?

Answer 6

The first code simply converts the sum of function arguments to it's binary representation as follow:
To convert a number to binary form we must take modules of number by 2 and then reduce that number for next step. In this example for sum = 3 we have:
3%2=1. So the least significant digit of binary form is 1. To continue we must reduce the number as:
[3/2]=1
(And this is a general rule for other basements too (remeber your question and ruduction in base 10))
And continue this process until sum become 0.

Answer 7

Alright, I got that so how about the other two programs

Answer 8

Alright, maybe I'll understand better by helping me out with this question Ahmadjon Boboev, Qasem and Airree,
https://www.sololearn.com/Discuss/1882877/?ref=app