Basic Syntax on for statements

#1

I notice that in the first few exercises teaching syntax, the last phrase within the parenthesis jumps from counter=++ to i=i+1. Now, i understand the substitution for counter with i, but why the change in the last phrase with no explanation? What does the change represent if anything at all?

#2

Basic `for` statement

``````for (var i = 1; i < 21; i++) {
// loop code body
}``````

The statement takes three parameters:

``````1. iterator variable declaration and initialization => Start
2. conditional expression                           => End
3. increment/decrement expression                   => Step``````

Your question concerns #3, the Step. This can be any expression that modifies the iterator value, and it can be in either direction, up or down the number line.

We can start with a higher value, and work backwards through a set of numbers with a negative step.

``````// count down by 5's
for (var i = 50; i > 0; i -= 5) {
console.log(i);
}``````

Output

``````50
45
40
35
30
25
20
15
10
5``````

We use a shorthand arithmetic assignment operator above, `-=`. The expression,

``i -= 5``

is the equivalent to,

``i = i - 5``

In both cases, `i` has `5` taken away.

This expression,

``i++``

is equivalent to,

``i = i + 1``

and this,

``i--``

is the same as,

``i = i - 1``

It is touched upon, but only briefly in the track. We do get plenty of practice though, so any confusion around this should clear up, presently. In the meantime, search for `JavaScript arithmetic operators` and visit the MDN link that comes up in the SERP.

#3

Thank you. I should have waited a few more lessons when this explained itself. Thank you for the response.