C# Variables

In C#, variables contain data values of specific data types.

Syntax

<data type>　<variable name>　=　<value>;

The following declares and initializes an int type variable.

int　num　=　100;

Above, int is the data type, num is the variable name (identifier). The = operator is used to assign a value to a variable. The value on the right side of the = operator is the value assigned to the variable on the left. In the above example, the value of 0 is assigned to the variable num.100 assigned to the variable num.

The following statements declare and initialize variables of different data types.

int　num　=　100;
float　rate　=　10.2f;
decimal　amount　=　100.50M;
char　code　=　'C';
bool　isValid　=　true;
string　name　=　"Steve";

The following are the naming conventions for declaring variables in C#:

• Variable names must be unique.

• Variable names can only contain letters, numbers, and underscores _.

• Variable names must start with a letter.

• Variable names are case-sensitive, num and Num are considered different names.

• Variable names cannot contain reserved keywords. If you want to use a reserved keyword as an identifier, you must add the @ prefix before the keyword .

C# is a strongly typed language. This means you can assign values of specified data types. You cannot assign an integer value to a string type, and vice versa.

int　num　=　"Steve";

Variables can be declared first and then initialized.

int　num;
num　=　100;

A value must be assigned to a variable before it is used; otherwise, C# will give a compile-time error.

int　i;
int j = i;　//Compile-time error: Use of uninitialized local variable “　i”

The value of a variable can be changed at any time after initialization.

int　num　=　100;
num　=　200;
Console.WriteLine(num);　//Output:200

Multiple variables of the same data type can be declared and initialized in the same line, separated by commas.

int　i,　j　=　10,　k　=　100;

Multiple variables of the same type can also be declared in multiple lines, separated by commas. The compiler will treat it as a single statement until a semicolon is encountered;.

int i = 0,　
　　　　j =　10,　
　　　　k =　100;

You can assign the value of a variable to another variable of the same data type. However, you must assign a value to it before using the variable.

int i =　100;
int j = i;　//　The value of j is100

In C#, variables are classified based on how they are stored in memory. Variables can be value types, reference types, or pointer types.

You do not have to specify a specific type when declaring variables. Use the var keyword instead of a data type. Learn about it next.