C# Intro

What is C#?

C# is pronounced "C-Sharp".

It is an object-oriented programming language created by Microsoft that runs on the .NET Framework.

C# has roots from the C family, and the language is close to other popular languages like C++ and Java.

The first version was released in year 2002. The latest version, C# 11, was released in November 2022.

C# is used for:

• Mobile applications
• Desktop applications
• Web applications
• Games
• VR
• Database applications
• And many more!

Why C#?

• It is one of the most popular programming language in the world

• It is easy to learn and simple to use

• It has a huge community support

• C# is an object oriented language which gives a clear structure to programs and allows code to be reused, lowering development costs

• As C# is close to C, C++ and Java, it makes it easy for programmers to switch to C# or vice versa




C# Syntax

C# Example

In the previous chapter, we discussed C# introduction, and we used the following code to print "Hello World" to the screen:


using System;

namespace HelloWorld
{
  class Program
 {
    static void Main(string[] args)
  {
      Console.WriteLine("Hello World!");
   }
  }
}



Result:
Hello World!

C# Example explained

Line 1: using system means that we can use classes from the System namespace.

Line 2: A blank line. C# ignores white space. However, multiple lines makes the code more readable.

Line 3: namespace is used to organize your code, and it is a container for classes and other namespaces.

Line 4: The curly braces {} marks the beginning and the end of a block of code.

Line 5: class is a container for data and methods, which brings functionality to your program. Every line of code that runs in C# must be inside a class. In our example, we named the class Program.

Don't worry if you don't understand how using System, namespace and class works. Just think of it as something that (almost) always appears in your program, and that you will learn more about them in a later chapter.

Line 7: Another thing that always appear in a C# program, is the Main method. Any code inside its curly brackets {} will be executed. You don't have to understand the keywords before and after Main. You will get to know them bit by bit while reading this tutorial.

Line 9: Console is a class of the System namespace, which has a WriteLine() method that is used to output/print text. In our example it will output "Hello World!".

If you omit the using System line, you would have to write System.Console.WriteLine() to print/output text.

Note: Every C# statement ends with a semicolon ; .

Note: C# is case-sensitive: "MyClass" and "myclass" has different meaning.

Note: Unlike Java, the name of the C# file does not have to match the class name, but they often do (for better organization). When saving the file, save it using a proper name and add ".cs" to the end of the filename. To run the example above on your computer, make sure that C# is properly installed: Go to the Get Started Chapter for how to install C#. The output should be:

Hello World!



C# Output

C# Output

To output values or print text in C#, you can use the WriteLine() method:


Example

Console.WriteLine("Hello World!");




You can add as many WriteLine() methods as you want. Note that it will add a new line for each method:


Example

Console.WriteLine("Hello World!");
Console.WriteLine("I am learner");
Console.WriteLine("Its awesome!");




You can also output numbers, and perform mathematical calculations:


Example

Console.WriteLine(1+2);




The Write Method

There is also a Write() method, which is similar to WriteLine().
The only difference is that it does not insert a new line at the end of the output:


Example

Console.Write("Hello World!");
Console.Write("Print in the same line");



Note that we add an extra space when needed (after "Hello World!" in the example above), for better readability.

In this tutorial, we will only use WriteLine() as it makes it easier to read the output of code.



C# Comments

C# Comments

Comments can be used to explain C# code, and to make it more readable. It can also be used to prevent execution when testing alternative code.

Single-line Comments

Single-line comments start with two forward slashes (//).

Any text between // and the end of the line is ignored by C# (will not be executed).

This example uses a single-line comment before a line of code:


Example

// This is comment
Console.Write("Hello World!");



This example uses a single-line comment at the end of a line of code:


Example

Console .Write( "Hello World!" ); // This is comment



C# Multi-line Comments

Multi-line comments start with /* and ends with */.

Any text between /* and */ will be ignored by C#.

This example uses a multi-line comment (a comment block) to explain the code:


Example

/* This is
a comment*/
Console .Write( "Hello World!" );



It is up to you which you want to use. Normally, we use // for short comments, and /* */ for longer.



C# Variables

C# Variables

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;




Where type is a C# type (such as int or string), and 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:


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:


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:


Example

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:


Example

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




Other Types

A demonstration of how to declare variables of other types:


Example

int myNum = 15 ;
double myDoubleNum = 5.99D ;
char myLetter = 'A'
bool myBool = true ;
string myText = "Hello" ;




You will learn more about data types in a later chapter.

C# Constant

Constant

If you don't want others (or yourself) to overwrite existing values, you can add the const keyword in front of the variable type.

will declare the variable as "constant", which means unchangeable and read-only:


Example

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




The conts 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.


C# Display Variables

Display Variables

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

To combine both text and a variable, use the + character:


Example

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




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


Example

string firstName = "John" ;
string lastName = "Miller ;
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):


Example

int x = 5 ;
int y = 10 ;
 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 10
• Then we use the WriteLine() method to display the value of x + y, which is 15

C# Display Variables

Declare Many Variables

To declare more than one variable of the same type, use a comma-separated list:


Example

int x = 5 , y = 6 , z = 7 ;
Console.WriteLine( x + y + z);




You can also assign the same value to multiple variables in one line:


Example

int x , y , z ;
x = y = z = 20;
 Console.WriteLine( x + y + z);




C# Identifiers

C# Identifiers

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:


Example

//Good
int minutesPerHour = 60 ;

//OK, but not so easy to understand what m actually is
int m = 60 ;




The general rules for naming variables 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 int and double) cannot be used as names


C# Data Types

C# Data Types

As explained in the variables chapter, a variable in C# must be a specified data type:

Example

int myNum = 15 ; // Integer (whole number)
double myDoubleNum = 5.99D ; // Floating point number
char myLetter = 'A' ; // Character
bool myBool = true ; // Boolean
string myText = "Hello" ; // String




A data type specifies the size and type of variable values.

It is important to use the correct data type for the corresponding variable; to avoid errors, to save time and memory, but it will also make your code more maintainable and readable. The most common data types are:


Data Type    
 Size        
 Description    
int
4 bytes
Stores whole numbers from -2,147,483,648 to 2,147,483,647
long
8 bytes
Stores whole numbers from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
float
4 bytes
Stores fractional numbers. Sufficient for storing 6 to 7 decimal digits
double
8 bytes
Stores fractional numbers. Sufficient for storing 15 decimal digits
bool
1 bit
Stores true or false values
char
2 bytes
Stores a single character/letter, surrounded by single quotes
string
2 bytes per
character
Stores a sequence of characters, surrounded by double quotes


Numbers

Number types are divided into two groups:

Integer types stores whole numbers, positive or negative (such as 123 or -456), without decimals. Valid types are int and long. Which type you should use, depends on the numeric value.

Floating point types represents numbers with a fractional part, containing one or more decimals. Valid types are float and double.

Even though there are many numeric types in C#, the most used for numbers are int (for whole numbers) and double (for floating point numbers). However, we will describe them all as you continue to read.

Integer Types

Int

The int data type can store whole numbers from -2147483648 to 2147483647. In general, and in our tutorial, the int data type is the preferred data type when we create variables with a numeric value.


Example

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




Long

The long data type can store whole numbers from -9223372036854775808 to 9223372036854775807. This is used when int is not large enough to store the value. Note that you should end the value with an "L":


Example

long myNum = 1500000L ;
Console .WriteLine( myNum );




Floating Point Types

You should use a floating point type whenever you need a number with a decimal, such as 9.99 or 3.14515.

The float and double data types can store fractional numbers. Note that you should end the value with an "F" for floats and "D" for doubles:


Float Example

float myNum = 15.57F ;
Console .WriteLine( myNum );





Double Example

double myNum = 19.39D ;
Console .WriteLine( myNum );




Use float or double?

The precision of a floating point value indicates how many digits the value can have after the decimal point. The precision of float is only six or seven decimal digits, while double variables have a precision of about 15 digits. Therefore it is safer to use double for most calculations.


Scientific Numbers

A floating point number can also be a scientific number with an "e" to indicate the power of 10:


Example

float f1 = 35e3F ;
double d1 = 12E4D ;
Console .WriteLine( f1 );
Console .WriteLine( d1 );




Booleans

A boolean data type is declared with the bool keyword and can only take the values true or false:


Example

bool isEatingFun = true ;
bool isCodingFun = False ;
 Console.WriteLine(isEatingFun);
Console.WriteLine(isCodingFun);




Boolean values are mostly used for conditional testing, which you will learn more about in a later chapter.

Characters

The char data type is used to store a single character. The character must be surrounded by single quotes, like 'A' or 'c':


Example

char myGrade = 'A' ;
Console .WriteLine( myGrade );




Strings

The string data type is used to store a sequence of characters (text). String values must be surrounded by double quotes:


Example

string greeting = "Hello World!" ;
Console .WriteLine( greeting );





Test Yourself With Quizzes

Click Button to take quiz