In today’s post, I want to address the usage of global variables. Global variables are variables that can be accessed from anywhere, hence the term, ‘global’. So every piece of code, every function, can access a global variable. Because of this, it is a good practice to have as few global variables as possible. This helps protect your data and in OOP circles is known as encapsulation. That being said, there are times when you need a global variable.
Imagine you have a program and want to keep track of the status of that program. You could create a global status variable to house the data to check on the status. Say, for example, you are requesting that the user put in their age. You could have a variable entitled, “userAge” and set the initial value to -1. Setting it to negative one allows you to test to see if the value has been set with an if statement because nobody is -1 years of age (excluding your annoying little brother).
Many times, booleans are used in this manner. Imagine that you have a form where the user is registering for your site. You have certain restrictions on the password. You can have a global variable set to false. When the end user finishes typing in their password information, you can test the user-supplied info against your requirements. If it passes, then you can set your password checking global variable to true. You can then use this global status variable to check to see if it is ok to submit the form.
So, bottom-line…try to keep global variables to a minimum, but do not hesitate to use them if necessary.