C# - Basic Syntax

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C# is an object-oriented programming language. In Object-Oriented Programming methodology, a program consists of various objects that interact with each other by means of actions. The actions that an object may take are called methods. Objects of the same kind are said to have the same type or, are said to be in the same class.

Basic Structure of a C# Program

Every C# program has a basic structure. Heres a simple example:

Example

For example, let us consider a Rectangle object. It has attributes such as length and width. Depending upon the design, it may need ways for accepting the values of these attributes, calculating the area, and displaying details.

Let us look at implementation of a Rectangle class and discuss C# basic syntax −

using System;

namespace RectangleApplication {
   class Rectangle {
      
      // member variables
      double length;
      double width;
      
      public void Acceptdetails() {
         length = 4.5;    
         width = 3.5;
      }
      public double GetArea() {
         return length * width; 
      }
      public void Display() {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }
   class ExecuteRectangle {
      static void Main(string[] args) {
         Rectangle r = new Rectangle();
         r.Acceptdetails();
         r.Display();
         Console.ReadLine(); 
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Length: 4.5
Width: 3.5
Area: 15.75

C# Syntax Rules: The Fundamentals

1. Case Sensitivity

C# is case-sensitive, meaning that variable names with different capitalization are treated as separate variables.

In the following example, we are demonstrating case sensitivity:

int Age = 30;
int age = 25;
Console.WriteLine(Age); // Output: 30
Console.WriteLine(age); // Output: 25

2. Every Statement Ends with a Semicolon (;)

All statements in C# must end with a semicolon to indicate the end of a command.

In the following example, we are showing the use of semicolons:

int x = 10;
Console.WriteLine(x); // Output: 10

3. Curly Braces {} Define Code Blocks

Curly braces group statements together in functions, loops, and conditional statements.

In the following example, we are using curly braces in an if statement:

int x = 7;
if (x > 5)
{
    Console.WriteLine("x is greater than 5"); // Output: x is greater than 5
}

4. Indentation & Whitespace

C# ignores extra spaces and newlines, but proper indentation makes the code more readable.

In the following example, we are using indentation to improve readability:

int x = 5;
int y = 10;
Console.WriteLine(x + y); // Output: 15

The using Keyword

The first statement in any C# program is

using System;

The using keyword is used for including the namespaces in the program. A program can include multiple using statements.

The class Keyword

The class keyword is used for declaring a class.

Comments in C#

Comments are used for explaining code. Compilers ignore the comment entries. The multiline comments in C# programs start with /* and terminates with the characters */ as shown below −

/* This program demonstrates
The basic syntax of C# programming 
Language */

Single-line comments are indicated by the '//' symbol. For example,

}//end class Rectangle    

Member Variables

Variables are attributes or data members of a class, used for storing data. In the preceding program, the Rectangle class has two member variables named length and width.

Member Functions

Functions are set of statements that perform a specific task. The member functions of a class are declared within the class. Our sample class Rectangle contains three member functions: AcceptDetails, GetArea and Display.

Instantiating a Class

In the preceding program, the class ExecuteRectangle contains the Main() method and instantiates the Rectangle class.

Identifiers

An identifier is a name used to identify a class, variable, function, or any other user-defined item. The basic rules for naming classes in C# are as follows −

• A name must begin with a letter that could be followed by a sequence of letters, digits (0 - 9) or underscore. The first character in an identifier cannot be a digit.

• It must not contain any embedded space or symbol such as? - + ! @ # % ^ & * ( ) [ ] { } . ; : " ' / and \. However, an underscore ( _ ) can be used.

• It should not be a C# keyword.

C# Keywords

Keywords are reserved words predefined to the C# compiler. These keywords cannot be used as identifiers. However, if you want to use these keywords as identifiers, you may prefix the keyword with the @ character.

In C#, some identifiers have special meaning in context of code, such as get and set are called contextual keywords.

The following table lists the reserved keywords and contextual keywords in C# −

C# Control Flow Statements

Conditional Statements

Control statements like if, else, and switch determine the flow of a program.

In the following example, we are checking voting eligibility using an if-else statement:

int age = 18;
if (age >= 18)
{
    Console.WriteLine("You are eligible to vote."); // Output: You are eligible to vote.
}
else
{
    Console.WriteLine("You are not eligible to vote.");
}

Looping Constructs

Loops help execute code multiple times.

For Loop

In the following example, we are using a for loop to print iterations:

for (int i = 1; i 
When the above code is compiled and executed, it produces the following result −
Iteration: 1
Iteration: 2
Iteration: 3


While Loop
In the following example, we are using a while loop to print count values:
int count = 1;
while (count <= 3)
{
    Console.WriteLine("Count: " + count);
    count++;
}

When the above code is compiled and executed, it produces the following result −
Count: 1
Count: 2
Count: 3

C# Data Input & Output
Printing Output to Console
You can use use Console.WriteLine() to display text in the console.
In the following example, we are printing a message:
Console.WriteLine("Welcome to C#"); // Output: Welcome to C#

Taking User Input
You can use the Console.ReadLine() to take input from the user.
In the following example, we are asking the user for their name and displaying it:
Console.Write("Enter your name: ");
string name = Console.ReadLine();
Console.WriteLine("Hello, " + name + "!");

When the above code is compiled and executed, it produces the following result ((depends on user input)) −
Enter your name: Alice
Hello, Alice!


Error Handling in C#
Use try-catch blocks to handle errors gracefully.
In the following example, we are handling an invalid conversion error:
try
{
    int num = Convert.ToInt32("ABC"); // Error: Cannot convert string to int
}
catch (Exception ex)
{
    Console.WriteLine("Error: " + ex.Message);
}
    
When the above code is compiled and executed, it produces the following result −
Error: Input string was not in a correct format.

C# Syntax Best Practices
The following are the best practices you should follow while writing C# code to make it clear, readable, and maintainable:
  

• Use meaningful variable names (e.g., customerName instead of cn) so the code is easy to understand.
• Follow C# naming rules (use camelCase for variables and PascalCase for classes) to keep code consistent.
• Keep your code readable by using proper indentation and adding comments where needed.
• Avoid hardcoding values; instead, use constants or configuration files for flexibility.
• Always handle errors properly using try-catch blocks to prevent crashes.