csharp_lexical_structure.md - brainchildservices/curriculum GitHub Wiki

SLIDE-1

C# lexical structure
- Computer languages, like human languages, have a lexical structure. A source code of a C# program consists of tokens. Tokens are atomic code elements. In C#, we have comments, variables, literals, white spaces, operators, delimiters, and keywords.
- C# programs are composed of characters from the Unicode character set.

SLIDE-2

C# comments
- Comments are used by humans to clarify the source code.
- There are three types of comments in C#.
  - Single-line comments
  - multi-line comments
  - XML comments.
- XML comments can be extracted to HTML files.
- Multi-line comments are enclosed by /* */ characters.
- Single line comments start with two forward slashes.

SLIDE-2(DOWNWARDS)

                USE A CODE EDITOR AND SEE COMMETED SECTION
                
                using System;

                /*
                    This is comments.cs
                    Author: Jan Bodnar                      
                    ZetCode 2021
                */

                namespace Comments
                {
                    // Program starts here
                    class Program
                    {
                        static void Main(string[] args)
                        {
                            Console.WriteLine("This is Comments program");
                        }
                    }
                }

Comments are ignored by C# compiler.

SLIDE-3

C# white space
- White space in C# is used to separate tokens in the source file.
- It is also used to improve readability of the source code.
- White spaces are required in some places. For example between the int keyword and the variable name.
- In other places, white spaces are forbidden.
- The amount of space put between tokens is irrelevant for the C# compiler.

SLIDE-4

C# variables
- A variable is an identifier which holds a value.
- In programming we say that we assign a value to a variable.
- Technically speaking, a variable is a reference to a computer memory where the value is stored.
- Variable names can have alphanumerical characters and underscores.
- An identifier may begin with a character or an underscore. It may not begin with a number.
- Variable names are case sensitive. This means that Name, name, and NAME refer to three different variables.(Advantage of C# language)

SLIDE-4(DOWNWARDS)

                string name23;
                int _col;
                Date birth_date;

                These are valid C# identifiers.


                string 23name;
                int %col;
                Date birth date;

                These are invalid C# identifiers.

SLIDE-5

C# literals
- A literal is a textual representation of a particular value of a type.
- Literal types include boolean, integer, floating point, string, character, and date.
- Technically, a literal will be assigned a value at compile time, while a variable will be assigned at runtime.

SLIDE-6

C# operators
- An operator is a symbol used to perform an action on some value.
- Operators are used in expressions to describe operations involving one or more operands.

SLIDE-7

C# separators
- A separator is a sequence of one or more characters used to specify the boundary between separate, independent regions in plain text or other data stream.
```
           [ ]   ( )   { }   ,   :   ;

           string language = "C#";
```
  - The double characters are used to mark the beginning and the end of a string.
  - The semicolon (;) character is used to end each C# statement.
  - Parentheses (round brackets) are used to mark the method signature. The signature consists of method parameters.
  - Curly brackets are used to denote the evaluated value.
  - Square brackets [] are used to denote an array type. They are also used to access or modify array elements.
  - Curly brackets {} are also used to initiate arrays.
  - Curly brackets are also used in variable interpolation or to enclose the body of a method or a class.
  - The comma character can be used to use multiple declarations on the same line of code.

SLIDE-8

C# keywords
- A keyword is a reserved word in the C# language.
- Keywords are used to perform a specific task in the computer program.
- For example, define variables, do repetitive tasks, or perform logical operations.
- C# is rich in keywords.
  - The keywords include if, else, for, while, base, false, float, catch, this, and many others.
  - The using, public, static, void, int, and for are C# keywords.
REF Link:
- https://zetcode.com/lang/csharp/lexis/