Introduction to Computer Programming

Computer Programming

• Computer programming is a process that includes coding, maintaining, updating, debugging, writing, and designing.
• It involves a set of instructions for the computer to perform different tasks.
• There are three types of errors that can occur during program execution:
  • Syntax errors: occur when the program violates one or more grammatical rules of the programming language.
  • Runtime errors: occur when the computer is directed to perform an illegal operation.
  • Logical errors: occur when a program implements a wrong logic.

Variables and Data Types

• Variables are named memory locations that store program’s input and its computational results during program execution.
• Variables can be classified into two types:
  • Number variables: store numeric values.
  • String variables: store a sequence of characters.
• Data types are data storage formats that can contain a specific type or range of values.
• In .NET, there are two types of data types:
  • Value type: contains the data directly, and each variable must be assigned a specific data type.
  • Reference type: stores the memory address of a variable, and is allocated on the heap.

Control Structures

• Loops are used to execute a set of statements repeatedly.
• There are three types of loops:
  • FOR…NEXT Loop: used to repeat a set of statements a specific number of times.
  • WHILE…WEND Loop: used to repeat an action until an associated condition becomes false.
  • Nested Loop: a loop within a loop.
• Conditional statements are used to make decisions in a program.
• Switch-case statements are used to handle multiple choices and transfer control to the case statements within its body.

Functions and Subroutines

• A function is a block of code that performs a specific task and returns a value.
• A subroutine is a self-contained set of statements that can be used from anywhere in a program.
• Parameters are used to provide input to a function or subroutine.
• There are four types of parameters in C#:
  • Value type: does not need the ref keyword.
  • Reference type: needs the ref keyword.
  • Output type: needs the out keyword.
  • Optional parameter: allows neglecting parameters with default values.

Debugging and Testing

• Debugging is the process of finding and removing errors in a program.
• Testing is a process of checking the quality of a program.
• Reasons for testing include:
  • Proper working
  • Satisfying quality
  • Fulfilling user requirements
  • Implementability
• Beta version is a version of software that is not ready for release and can be changed after user feedback.

Object-Oriented Programming

• Abstraction is the process of showing only the necessary information to the outside world.
• Encapsulation is the process of hiding the implementation details of an object from the outside world.
• Polymorphism is the ability of an object to take on multiple forms.
• Inheritance is the process of creating a new class based on an existing class.
• C# is a language that meets all the requirements of OOPs.### Object-Oriented Programming
• A typical program in an object-oriented language like C# consists of multiple objects interacting dynamically.
• Class and Struct are user-defined data types, but they have significant differences:
  • Struct is a value type, inherits from System.ValueType, and is usually used for smaller amounts of data.
  • Struct can't be inherited, abstract, or have a default constructor.
  • Class is a reference type, inherits from System.Object, and is usually used for larger amounts of data.
  • Class can be inherited, abstract, and have a default constructor.

Abstract Class vs Interface

• An abstract class is a special kind of class that cannot be instantiated, but can be inherited from.
• Abstract classes are used to define the core identity of a class and are used for objects of the same type.
• An interface contains only the signatures of methods, properties, events, or indexers, and must be implemented by classes that implement it.
• Interfaces are used to define peripheral abilities of a class and can be implemented by multiple classes.
• Key differences between abstract classes and interfaces:
  • Multiple inheritance: a class can implement multiple interfaces but can only inherit from one abstract class.
  • Default implementation: an abstract class can provide complete, default code, while an interface cannot.

Enum

• An enum is a value type with a set of related named constants.
• Enums are strongly typed and cannot be implicitly assigned to another enum type, even if the underlying value is the same.
• Enums are used to create numeric constants in .NET framework.
• Default type of an enum is int, but can be changed to other types like byte, sbyte, short, ushort, uint, long, or ulong.

Break and Continue Statements

• Break statement is used to exit a loop or switch statement.
• Continue statement is used to skip the current iteration and move to the next iteration in a loop.

Hash Table

• A hash table is a collection that stores key-value pairs.
• Keys are used to find the storage location and are immutable and cannot have duplicate entries.
• Hash codes are generated automatically when items are added to a hash table.
• Hash table is a general-purpose dictionary collection, and each item is a DictionaryEntry object with two properties: a key object and a value object.

LINQ

• LINQ stands for Language Integrated Query.
• LINQ is a data querying methodology that provides querying capabilities to .NET languages with syntax similar to a SQL query.
• LINQ can query any source of data, including collections of objects, databases, or XML files.
• Advantages of LINQ:
  • Object-based, language-integrated way to query over data.
  • Compile-time syntax checking.

Reflection

• Reflection is the process of runtime type discovery to inspect metadata, CIL code, late binding, and self-generating code.
• Reflection can be used to access the same "type" information as displayed by the ildasm utility at design time.
• System.Reflection namespace contains numerous related types, including:
  • Assembly
  • AssemblyName
  • EventInfo
  • PropertyInfo
  • MethodInfo

Expression and Expression Trees

• Expression and Expression Trees are classes that can represent C# code as data.
• Expressions are non-compiled data about the code, unlike Func or Action.
• Most LINQ Providers have been built using Expressions.

Object, Var, and Dynamic

• Object: introduced with C# 1.0, can store any kind of value, but requires casting to use.
• Var: introduced with C# 3.0, can store any type of value, is type-safe, and requires initialization at declaration.
• Dynamic: introduced with C# 4.0, can store any type of variable, is not type-safe, and can cause problems at runtime.

Class and Object

• Class is a collection of objects.
• Object is a real-time entity that can perform a set of related activities.
• Class is composed of three things: name, attributes, and operations.

Encapsulation

• Encapsulation is a process of binding data members and member functions into a single unit.
• Class is an example of encapsulation.

Palindrome and Armstrong Numbers

• Palindrome number is a number that remains the same when its digits are reversed.
• Armstrong number is a number that is equal to the sum of cubes of its digits.

Reversing a Number

• Reversing a number can be done using loop and arithmetic operators.### C# Programs

• A C# program can be used to print any multiplication table until a given number.

• A program can be written to print the characters in a string in reverse order using the Reverse() function and a foreach loop.

Menu-Driven Program

• A menu-driven program can be created to perform arithmetic operations (addition, subtraction, multiplication, and division) using a switch statement and user input.

Sorting and Printing Names

• A C# program can be written to sort a list of names in both ascending and descending order using the Array.Sort() method and Array.Reverse() method.
• A program can be used to print unique names by removing duplicate entries from a list of names using the Distinct() LINQ function.

Inserting Spaces Before Uppercase Letters

• A C# program can be written to insert a single space before every uppercase letter in a string using the char.IsUpper() method and a foreach loop.

Exception Handling

• A program should be designed to handle exceptions and provide meaningful error messages to the user.
• A program should continue to run until the user chooses to exit.

Finding Smallest and Largest Numbers in an Array

• A C# program can be written to find and print the smallest and largest numbers in a given integer array using the Array.Sort() method.
• The program should handle exceptions and provide meaningful error messages to the user.

Learn the basics of computer programming, including coding, maintaining, updating, and debugging. Understand the process of writing instructions for a computer to perform different tasks.