`index++`

adds 1 to the value of index and assigns it to index while evaluating to the value before adding 1. It is similar to `index = index + 1;`

There is a difference in that if you set index to 3 say; `index = 3;`

and then assign it to x like this `x = index++`

The value of x is 3 and the value of index is 4.

On the other hand `++index`

adds one to index and evaluates to the new value. So `index = 3;`

and then assign it to x like this `x = ++index`

The value of x is 4 and the value of index is also 4.

So be careful how you use `x++`

as an expression. It may not do what you think, `++x`

does what you think.

`index--`

is the same except subtract 1.