Explain please.

Question

for (var x=1; x<10; x++){
x+=x;
}
console.log(x); //output 15

//if we console x inside for loop the output comes like

for (var x=1; x<10; x++){
x+=x;
console.log(x);
} //output 2 6 14

Answer 1

Safaa Alnabhan
The third statement of the loop, in your case the x++ is executed last.
So if you have this loop
for (var x = 1; x < 10; x++) {
x += x;
console.log(x);
}
It can be written like this
for (var x = 1; x < 10;) {
x += x;
console.log(x);
x++;
}
Notice that I move the x++ statement. So when the x reach 14, it will be written to the console, but the x++ statement is executed afterward, so the final value of x, 15, won't be written to the console

Answer 2

Agent_I
I got a bit confused there thinking the `x++` instruction will only be executed when condition `x < 10` yields true. But a little test I did in several languages (having similar syntax) proves the output was the same.

Answer 3

[Begin loop]
Let x be 1, repeat increasing x while x is less than 10

x += x // x is now 2 (1+1)
Is x less than 10? (Yes)
x++ // x is now 3 (2+1)

x += x // x is now 6 (3+3)
Is x less than 10? (Yes)
x++ // x is now 7 (6+1)

x += x // x is now 14 (7+7)
Is x less than 10? (No)
[Exit loop]

I hope this explains the original question above.

Answer 4

Ipang thank you for answering .. the orginal question is about the first for loop why we got 15 not 14

Answer 5

For the second for loop I know how we get that result

x=1+1=2
x=2+1+3=6
x=6+1+7 =14

But why we get a different output when we console x outside the loop .. after looping x comes 14 that is bigger than 10 so we can't add 1 to the final result .. how did it become 15

Answer 6

This code shows what happens when you place the console.log inside a loop

Answer 7

//the same issue here and what about loop why we add x to x to 100 without any looping?
for(var x=1; x<10; x++){
x=x+x+100; console.log(x);
} //102
for(var x=1; x<10; x++){
x=x+x+100;
}
console.log(x); //103

Answer 8

Nico Ruder I didn't get what you meant

Answer 9

//the same issue here when we console x after looping x = 10 the output 10+10+100=120
var x=1;
for(x;x<10;x++){}
x+=x+100;
console.log(x);
//but when we console x inside for loop the final result of x = 9
var x=1;
for(x;x<10;x++){
console.log(x); } // 123456789

Answer 10

Ipang thank you for answering .. the orginal question is about the first for loop why we got 15 not 14

Answer 11

Ipang thank you for answering .. the orginal question is about the first for loop why we got 15 not 14