CSharp (C#) Language Reference

using System;

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

1:  using System; 
// is used for importing builtin library functionalities. Here also we can import namespace of our class libraries.

3:  namespace HelloWorld 
// namespace groups multiple class into a single group so that if we include that namespace into top of our code with using keyword then it includes all class library of that namespace.

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

5: class HelloWorld 
// C# is a Object Oriented Programming language. So we must write our method/function inside a class always. 

7: static void Main(string[] args) 
//Every C# program has static Main method. Application starts from that method. 
  
9: Console.WriteLine("Hello World!");  
//Will print Hello World! at black console window. 

// This is an example of single line comment
//Console.WriteLine("Hello World");
Console.WriteLine("learnersheaven.com");

Multi Line comment example
/*
var url = "https://learnersheaven.com";
var html = WebClient.DownloadText(url);
*/
var webClient = new System.Net.WebClient();
var html = webClient.DownloadString("https://learnersheaven.com");

int - stores integers (whole numbers), without decimals, such as 103 or -103
double - stores floating point numbers, with decimals, such as 10.99 or -20.99
char - stores single characters, such as 'a' or 'B'. Char values are surrounded by single quotes
string - stores text, such as "Hello World". 
bool - stores values with two states: true or false

int totalValue = 10;
double sum = 20.50;
char firstChar = 'A';
string firstName = "Learners";
bool isDone = true;

int myInt = 12;
double myDouble = myInt;       // Automatic casting: int to double
Console.WriteLine(myInt);      // Outputs 12
Console.WriteLine(myDouble);   // Outputs 12

double myDouble = 10.78;
int myInt = (int) myDouble;  // Manual casting: double to int
Console.WriteLine(myDouble); // Output 10.78
Console.WriteLine(myInt);    // Output 10

/* String input */
// Type your username and press enter
Console.WriteLine("Enter username:");
// Create a string variable and get user input from the keyboard and store it in the variable
string userName = Console.ReadLine();
// Print the value of the variable (userName), which will display the input value
Console.WriteLine("Username is: " + userName);

/* Number input */
Console.WriteLine("Enter your age:");
int age = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Your age is: " + age);

int x = 100 + 50;        // 150 (100 + 50)
int sum1 = x + 250;      // 400 (150 + 250)
int sum2 = x + sum1;     // 800 (400 + 400)

string txt = "Hello World";
Console.WriteLine(txt.ToUpper());   // Outputs "HELLO WORLD"
Console.WriteLine(txt.ToLower());   // Outputs "hello world"

//String Concatenation
string firstName = "John ";
string lastName = "Wick";
string name = firstName + lastName;
Console.WriteLine(name);  // Outputs John Wick

//String Interpolation
string firstName = "John";
string lastName = "Wick";
string name = $"My full name is: {firstName} {lastName}";
Console.WriteLine(name); // Outputs My full name is: John Wick

// Special Characters inside string
// Special characters are used inside a string after a back slash \
string txt = "We are learning \"C#\" at learnersheaven.com";

if (condition) 
{
  // block of code to be executed if the condition is True
}
else{
  //  block of code to be executed if the condition is False
}

int time = 20;
if (time < 10) 
{
  Console.WriteLine("Good morning.");
} 
else if (time <= 20) 
{
  Console.WriteLine("Good day.");
} 
else 
{
  Console.WriteLine("Good evening.");
}
// Outputs "Good day."

switch(expression) 
{
  case x:
    // code block
    break;
  case y:
    // code block
    break;
  default:
    // code block
    break;
}

int day = 4;
switch (day) 
{
  case 1:
    Console.WriteLine("Monday");
    break;
  case 2:
    Console.WriteLine("Tuesday");
    break;
  case 3:
    Console.WriteLine("Wednesday");
    break;
  case 4:
    Console.WriteLine("Thursday");
    break;
  case 5:
    Console.WriteLine("Friday");
    break;
  case 6:
    Console.WriteLine("Saturday");
    break;
  case 7:
    Console.WriteLine("Sunday");
    break;
}
// Outputs "Thursday" (day 4)

for(int i = 0; i < 100; i++){
	// code block to be execute  
}

int i = 1;
while (i < 10) 
{
  	// code block to be executed
	i++;
}

int j = 0;
do  
{
  // code block to be executed
  j++;
}while(j < 10)

var list = new[]{1,2,3,4,5,6,7,8,9,10};
foreach( var i in list){
	// Code block to be execute
}

for (int i = 0; i < 10; i++) 
{
  if (i == 4) 
  {
    break;
  }
  Console.WriteLine(i);
}

for (int i = 0; i < 10; i++) 
{
  if (i == 4) 
  {
    continue;
  }
  Console.WriteLine(i);
}

string[] cars;
string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Console.WriteLine(cars[0]);

foreach( var c in cars){
 	 Console.WriteLine(c);
}