Changes

This is a somewhat abstract concept, but let’s assume I’ve got a handwritten piece of paper and a friend wants to borrow it. If I make a copy of this piece of paper, and give the copy to my friend, I’m ''passing by value'' and anything that he writes on the paper will not affect my original version (since I gave him a copy). However, if I give the original version to my friend, I’m passing by reference, and any changes he make will change my original paper.

* If a variable is ''passed by value'', a copy of the variable is send leaving the original variable value intact.