Variables in Loops

CS Principles Unit and Lesson Discussion
1

We have begun Unit 5 Lesson 5 and one of my students had a great question this morning. Can you call a variable in a while/for loop out of the loop later?

I keep going back and forth…yes - no. Can anyone help?

2

First, tighten up the vocabulary. Variables are referenced. Functions are called. I don’t mean to single you out on this because I have to watch it too.

The short answer is maybe.

It all depends on the variable’s scope. In Unit 4 lesson 10 we learn about scope. Javascript scope wasn’t designed well. It is different than look alike languages C and Java. That may cause confusion.

If you do this:

for (var i = 0; i < 4; i++) {
  var x = i * 2;
  console.log(i);
}
console.log(i);
console.log(x);

i and x are both global variables and can be referenced anywhere. In this example 1, 2, 3, 4, and 6 will be printed in the log.

In this example:

function countToThree () {
  for (var i = 0; i < 4; i++) {
    var x = i * 2;
    console.log(i);
  }
}
countToThree();
console.log(i);
console.log(x);

i and x are defined within the function countToThree but nowhere else. An error is thrown for the last 2 lines because i and x are not defined.

Within scope constraints, all the variables can be referenced.

1 Like
3

Oops…yes, you are right about the vocabulary.

That makes sense! Thank you for your help!