Can a for loop increment/decrement by more than one?
JavascriptFor LoopIncrementJavascript Problem Overview
Are there other ways to increment a for
loop in Javascript besides i++
and ++i
? For example, I want to increment by 3 instead of one.
for (var i = 0; i < myVar.length; i+3) {
//every three
}
Javascript Solutions
Solution 1 - Javascript
Use the +=
assignment operator:
for (var i = 0; i < myVar.length; i += 3) {
Technically, you can place any expression you'd like in the final expression of the for loop, but it is typically used to update the counter variable.
For more information about each step of the for loop, check out the MDN article.
Solution 2 - Javascript
A for
loop:
for(INIT; TEST; ADVANCE) {
BODY
}
Means the following:
INIT;
while (true) {
if (!TEST)
break;
BODY;
ADVANCE;
}
You can write almost any expression for INIT
, TEST
, ADVANCE
, and BODY
.
Do note that the ++
operators and variants are operators with side-effects (one should try to avoid them if you are not using them like i+=1
and the like):
++i
meansi+=1; return i
i++
meansoldI=i; i+=1; return oldI
Example:
> i=0
> [i++, i, ++i, i, i--, i, --i, i]
[0, 1, 2, 2, 2, 1, 0, 0]
Solution 3 - Javascript
for (var i = 0; i < 10; i = i + 2) {
// code here
}
Solution 4 - Javascript
Andrew Whitaker's answer is true, but you can use any expression for any part.
Just remember the second (middle) expression should evaluate so it can be compared to a boolean true
or false
.
When I use a for
loop, I think of it as
for (var i = 0; i < 10; ++i) {
/* expression */
}
as being
var i = 0;
while( i < 10 ) {
/* expression */
++i;
}
Solution 5 - Javascript
for (var i = 0; i < myVar.length; i+=3) {
//every three
}
additional
Operator Example Same As
++ X ++ x = x + 1
-- X -- x = x - 1
+= x += y x = x + y
-= x -= y x = x - y
*= x *= y x = x * y
/= x /= y x = x / y
%= x %= y x = x % y
Solution 6 - Javascript
You certainly can. Others have pointed out correctly that you need to do i += 3
. You can't do what you have posted because all you are doing here is adding i + 3
but never assigning the result back to i
. i++
is just a shorthand for i = i + 1
, similarly i +=3
is a shorthand for i = i + 3
.
Solution 7 - Javascript
The last part of the ternary operator allows you to specify the increment step size. For instance, i++ means increment by 1. i+=2 is same as i=i+2,... etc. Example:
let val= [];
for (let i = 0; i < 9; i+=2) {
val = val + i+",";
}
console.log(val);
Expected results: "2,4,6,8"
'i' can be any floating point or whole number depending on the desired step size.
Solution 8 - Javascript
There is an operator just for this. For example, if I wanted to change a variable i by 3 then:
var someValue = 9;
var Increment = 3;
for(var i=0;i<someValue;i+=Increment){
//do whatever
}
to decrease, you use -=
var someValue = 3;
var Increment = 3;
for(var i=9;i>someValue;i+=Increment){
//do whatever
}