C# Variables and Constants

Variables

In the following example, message is the name of the variable that stores the string data value “Hello World!!“. As the name suggests, the contents of a variable can vary, i.e., you can change the value of a variable at any time.

namespace CSharpTutorials
{
    class Program
    {
        static void Main(string[] args)
        {
            string message = "Hello World!!";

            Console.WriteLine(message);
            Console.ReadLine();
        }
    }
}

Variables are containers for storing data values.

In C#, there are different types of variables (defined with different keywords), for example:

• int – stores integers (whole numbers), without decimals, such as 123 or -123
• double – stores floating point numbers, with decimals, such as 19.99 or -19.99
• char – stores single characters, such as ‘a’ or ‘B’. Char values are surrounded by single quotes
• string – stores text, such as “Hello World”. String values are surrounded by double quotes
• bool – stores values with two states: true or false

Declaring (Creating) Variables

To create a variable, you must specify the type and assign it a value:

Syntax

type variableName = value;

Examples

Create a variable called name of type string and assign it the value “John”:

string name = "John";
Console.WriteLine(name);

Create a variable that should store a number, called myNum of type int and assign it the value 15:

int myNum = 15;
Console.WriteLine(myNum);

You can also declare a variable without assigning the value, and assign the value later:

int myNum;
myNum = 15;
Console.WriteLine(myNum);

Note that if you assign a new value to an existing variable, it will overwrite the previous value.
Change the value of myNum to 20:

int myNum = 15;
myNum = 20; // myNum is now 20
Console.WriteLine(myNum);

Multiple Declarations

int i, j, k, l = 0;

int amount, num;

Multi-Line Declarations

int i, j, 
    k, 
    l = 0;

Variable Assignment

int i = 100;

int j = i; // value of j will be 100

Constants

You can add the const keyword before the type of your variable if you don’t want others (or yourself) to overwrite existing values (this will declare the variable as “constant”, which means unchangeable and read-only). The const keyword is useful when you want a variable to always store the same value.

const int myNum = 15;
myNum = 20; // error

Syntax for other types of variables

int myNum = 5;
double myDoubleNum = 5.99D;
char myLetter = 'D';
bool myBool = true;
string myText = "Hello";

Display variables

The WriteLine() method is often used to display variable values to the console window.

string name = "John";
Console.WriteLine("Hello " + name);

You can also use the + character to add a variable to another variable:

string firstName = "John ";
string lastName = "Doe";
string fullName = firstName + lastName;
Console.WriteLine(fullName);

For numeric values, the + character works as a mathematical operator (notice that we use int (integer) variables here):

int x = 5;
int y = 6;
Console.WriteLine(x + y); // Print the value of x + y