for loop with arithmetic expression

Question

Can I use arithmetic expressions in a for loop?

e.g.

<script>
   var i=2;

   for(i=2;i<10;i+2){
      document.write(i);
   }
</script>

You shouldn't be declaring the variable that you are using for the loop. Unless you need to use it elsewhere once the loop is done. — durbnpoisn
– durbnpoisn, Commented Jan 11, 2016 at 17:18
Yes you can. But i+2 by itself will compute i+2 and discard the results (the value of i won't change). Perhaps you mean i += 2. — lurker
– lurker, Commented Jan 11, 2016 at 17:22

melli-182 · Accepted Answer · 2016-01-11 17:35:20Z

5

The problem is not adding 2 to i, but that i+2 is not an assignment, so it will result in an infinite loop. You can write it like this:

var i;
for(i = 2; i < 10; i += 2){
  document.write(i);
}

i += 2 means "add 2 to i and store the result in i", basically twice i++.

Example fixed here.

Example with infinite loop here

edited Jan 11, 2016 at 17:35

melli-182

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answered Jan 11, 2016 at 17:17

Tobias

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Comments

Nina Scholz · Accepted Answer · 2016-01-11 17:17:14Z

2

With addition assignment:

The addition assignment operator adds the value of the right operand to a variable and assigns the result to the variable. The types of the two operands determine the behavior of the addition assignment operator. Addition or concatenation is possible. See the addition operator for more details.

for (i = 2; i < 10; i += 2) {
//                    ^^

Example:

var i =0;
for (i = 2; i < 10; i += 2) {
    document.write(i + '<br>');
}

answered Jan 11, 2016 at 17:17

Nina Scholz

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