4 Reasons Why You Need Private Variables in Your Code

If you’ve ever written any code, you’re probably familiar with variables. These are the tiny bits of text that store data in your program. They can be relatively simple, such as a number, or much more complex, such as an object that stores information and behaves differently depending on its assigned properties.

This is where variables come into play: programmers need them so that they can store data and pass it around between functions and other code sections in their programs without constantly copying that data from method to method.

By using private variables instead of public ones (which are visible to everyone), you are keeping this information hidden from anyone who does not have access or access rights to see what those specific variables hold.

What is a private variable?

unit test private methods

Variables help you to save temporary values for reuse later. They are different from constants, which you cannot change during execution. Variables are stored in memory, so they can be changed whenever you need them. If a variable is private, only the code that declared it could access it. If it’s public, anyone can use it.

You can use the private keyword to define a variable in C#. For example:

private string _documentName;

How do you know when to use variables and when constants are more appropriate? As a rule of thumb: variables should be used for data that changes frequently or is sensitive. You should use constants instead for data whose value does not change or is not sensitive enough to require privacy.

A private variable is a variable that’s not visible outside of a small section of code. It is called private because it is hidden from other classes.

Class members that can access private class variables in C# are:

  • private method (aka private function)
  • public method (aka public function)
  • protected method
  • virtual method
  • internal method
  • constructor
  • private property
  • public property

Class members that are prevented from accessing private variables:

  • parent class
  • child class
  • static method (if the variable itself is not defined as a private static variable)

Why do you need private variables?

Private variables are useful because they let you store data in a program that a specific place in the program can only access.

For example, if you are writing a program that counts items in a shopping cart, you don’t want other parts of the program to see the list of items or access that data. Private variables are the solution for keeping this section of code from seeing the items in the shopping cart.

Variables are an important part of any programming language. They allow you to store values and reuse them throughout your code. But not all variables are created equal. Some of them are public variables, meaning any part of your code can access them. Others are private, meaning they can only be accessed by the code that declares them.

Private variables can be useful if you want to prevent other parts of your code from accidentally changing the value of a variable or if you want to prevent them from accessing sensitive information.

In short, private variables give you more control over your code and can help make your code more reliable and secure.

There are four reasons to use private variables:

  1. Private variables are an easy way to keep track of the state of the class.
  2. Private variables allow you to reuse data specific to a particular class.
  3. Private variables hide data other classes shouldn’t see.
  4. Private variables reduce coupling.

Let’s discuss every reason in more detail.

Four reasons to use private variables

1. Private variables are an easy way to keep track of the state of the class – Private variables are an easy way to keep track of the state of the class. For example, if you want to know whether a button is pressed, you can check the private variable to see if it is true or false. Private variables are useful because they do not pollute the class’s public interface.

2. Private variables allow you to reuse data specific to a particular class – Without private variables, you would have to declare additional parameters for every value you want to pass from one private method to another. And having a long parameter list is a code smell: a potential problem in the code. The one that you can solve by having a Parameter object, but you still need to carry that data around.

3. Private variables hide data other classes shouldn’t see – Encapsulation is one of the most critical parts of object-oriented programming. Encapsulation prevents data from leaking out of a class. This makes the data available to the class’s methods but not the outside world. Private variables are essential in object-oriented programming since they allow you to have data that is only available to a single class.

4. Private variables reduce coupling – Coupling means that a change in one component requires changes in other components. For example, if you have class A and expose a variable to class B, then any change to the variable from class A means you must also change class B. As a result, you must change a lot of code to change one thing.

When to use the private variable?

A common programming error is forgetting to declare a variable as private. This may seem like a minor mistake if you’re new to programming. However, if you’re not careful, you could create a problem for yourself. As stated above, if another class uses the same variable, it can increase coupling between classes.

As a general rule, declare all variables as private by default. If you later need to expose them, use the getter and setter methods or properties to control access to the private variable. In C#, the common practice is to declare a property that encapsulates access to the private field.

So, remember: expose access to the private variable via property or a setter or getter method, but don’t ever expose the private members themselves!


You need to manage complexity in your code by ensuring you have the right access level. Private instance variables are accessible only in the same class. So if something goes wrong, there is only one source file to look at.

In object-oriented programming, one of the most important concepts is encapsulation. This is the idea that you should wrap up data and behavior together in an object, and that object should be responsible for hiding its internals from the rest of the program. This allows you to create an API for objects that is simple and easy to use while still keeping the internals of your objects hidden away.

One of the key ways that you achieve encapsulation in your objects is by using private variables. They allow you to hide the details of your object’s internals from the outside world and make it much easier to change them without breaking the API.

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