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:
type variableName = value;
Where type is a C# type (such as
variableName is the name of the variable (such as x or
name). The equal sign is used to assign values to the variable.
To create a variable that should store text, look at the following example:
Create a variable called name of type
string and assign it the value "John":
string name = "John"; Console.WriteLine(name);
To create a variable that should store a number, look at the following example:
Create a variable 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);
However, you can add the
const keyword 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):
const int myNum = 15; myNum = 20; // error
const keyword is useful when you want a variable to always store the same value, so that others (or yourself) won't mess up your code. An example that is often referred to as a constant, is PI (3.14159...).
Note: You cannot declare a constant variable without assigning the value. If you do, an error will occur: A const field requires a value to be provided.
A demonstration of how to declare variables of other types:
int myNum = 5; double myDoubleNum = 5.99D; char myLetter = 'D'; bool myBool = true; string myText = "Hello";
You will learn more about data types in the next chapter.
WriteLine() method is often used to
display variable values to the console window.
To combine both text and a variable, use the
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
From the example above, you can expect:
- x stores the value 5
- y stores the value 6
- Then we use the
WriteLine()method to display the value of x + y, which is 11
Declare Many Variables
To declare more than one variable of the same type, use a comma-separated list:
int x = 5, y = 6, z = 50; Console.WriteLine(x + y + z);
All C# variables must be identified with unique names.
These unique names are called identifiers.
Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).
Note: It is recommended to use descriptive names in order to create understandable and maintainable code:
// Good int minutesPerHour = 60; // OK, but not so easy to understand what m actually is int m = 60;
The general rules for constructing names for variables (unique identifiers) are:
- Names can contain letters, digits and the underscore character (_)
- Names must begin with a letter
- Names should start with a lowercase letter and it cannot contain whitespace
- Names are case sensitive ("myVar" and "myvar" are different variables)
- Reserved words (like C# keywords, such as
double) cannot be used as names