I don't know why I find it very hard to understand how the for...loop works.

Question

For instance I need an explanation on why the output of the code below is 25

var x = 0;
for (i=0; i < 5; ++i) {
x += 2;
x += 2;
}
x += i
console.log(x)

Answer 1

x and i starts off as 0.
in the each time the loop adds 4 to x. The loop runs 5 times: when it is 0, 1, 2, 3, 4. x will be 20, because 4*5 = 20.
The last part runs at the end of every loop, so when the loop executed for the 5th time, i was 4. But then it added one, so it became 5, and the condition wasn't true anymore so it stopped.
20 + 5 = 25, so the output is 25

Answer 2

Mofey

var x = 0;
for (i=0; i<5; ++i) {
x + = 2;
x + = 2; }
x += i
console.log(x)

When i = 0 then x = 4
//workings
for (i=0; i<5; ++i) {
x = 0 + 2; //firstly x = 2

//then
x = 2 + 2; // later x = 4
}

//now ( i = 0 and x = 4) and the loop will run again since "i" isn't up to 5

When i = 1 then x = 8
//workings
for (i=1; i<5; ++i) {
x = 4 + 2; //firstly x = 6

//then
x = 6 + 2; // later x = 8
}

//now ( i = 1 and x = 8) and the loop will run again since "i" isn't up to 5

When i = 2 then x = 12
//workings
for (i=2; i<5; ++i) {
x = 8 + 2; //firstly x = 10

//then
x = 10 + 2; // later x = 12
}

//now ( i = 2 and x = 12) and the loop will run again since "i" isn't up to 5

When i = 3 then x = 16
//workings
for (i=4; i<5; ++i) {
x = 12 + 2; //firstly x = 14

//then
x = 14 + 2; // later x = 16
}

//now ( i = 3 and x = 16) and the loop will run again since "i" isn't up to 5

Continue.......

Answer 3

When i = 4 then x = 20
//workings
for (i=4; i<5; ++i) {
x = 16 + 2; //firstly x = 18

//then
x = 18 + 2; // later x = 20
}

//now ( i = 4 and x = 20)

++i will increase "i" to 5 now and then check (i<5;) then the loop will stop...

So finally
x = 20
i = 5..

Now

x += i equals x = 20 + 5.

console.log(x)

//25

Answer 4

Mofey notice me when you find this book

Answer 5

Understand one thing that i have confused for a while understand that the condition inside the for loop is checked just before the body of the for loop is executed
var x = 0;
for (i=0; i < 5; ++i) {
x += 2;
x += 2;
}
x += i
console.log(x)
The last iteration of i becomes 5 but the body of the for loop will not be executed because the condition i<5 becomes false
and remember that i has a glopal scope and can be accessed outside the loop so i outside the becomes 5
You can try
console.log(i)
//5

Answer 6

Airree i agree with your explanation

Answer 7

Airree even though you explained it in the simplest possible form, it still took me the best of my understanding to assimilate that explanation. Thanks

Answer 8

I need someone to please recommend a book that could further broaden my horizon on for...loop

Answer 9

Why insted of
x +=2;
x +=2;

don’t do just one line of
x +=4;

????
i have hard time to uderstand it

var x = 0;
for (i=0; i < 5; ++i) {
x += 4;
}
x += i
console.log(x)

Answer 10

https://www.w3schools.com/js/js_loop_for.asp

Answer 11

for (i = 3; i<30; i++){...}

Can be thought as:

var i = 3;
(loop until break){
if (!(i < 30)){
break;
}
...
i++;
}

Answer 12

Here you have the instruction for(...) How you can see the variable for iterate i is 0 the first time i=0, and it will be incrementen by 1 (++i), while i <5, it means that i can take five values i = 0, 1, 2, 3 and 4, it means that the instructions corresponding yo the for(...) Will be repeated 4 times, as you can see x is incremented by 4, first time by 2 (x+=2) and second time (x+=2) also by 2, then you hace 4 repeated 5 times, it is 20, and next you add i (x += i), that hace the value of 5, and it is 25

Answer 13

The easiest way, is to create a table on the papper, in which you will write down the values, after every iteration. More specific, you will put the values of i , x, x', x result on the orizontal axe and the iteration values : 1,2,3,4,5 on the vertical axe. Your table can be a 4×5 , 4 cols ×5 rows. Good luck!

Answer 14

Thanks for respond ;) however I still dont get it. in your example 4 cols x 5 rows equal 20.. but answer is 25.. where the 5 coming from ?? ;(

Answer 15

Graphic Table
___________|_____x _____x'_____x"_____ x.result__
Iteration 1 |
Iteration 2 |
Iteration 4 |
Iteration 5 |

Answer 16

Thank You so much !!!!! you’re the Man :) I finally understood it, with make my day ;) enjoy rest of your day buddy ;) and happy coding. Again thanks 🙏 a lot 😉🙌