Harding University: Frank McCown's "Passing Arguments by Value and by Reference"
Read this article, which explains how data is passed between functions. When data is passed by value, the actual contents of the variable is passed. However, with some data, you may instead simply want the program to access the data directly from the current location where it is stored. To do this, you pass the value by reference, which tells the function to access the address of the variable.
Click http://web.archive.org/web/20161110160528/http://www.harding.edu/fmccown/classes/comp151-s14/notes/notes19.html link to open resource.