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.