C# Programming Basics

C# Introduction

• C-Sharp is an object-oriented programming language from Microsoft, running on the .Net Framework
• It has features like strong typing, imperative and declarative programming

C# History

• In 1999, Anders Hejlsberg assembled a team to create a language called "Cool"
• July 2000: Project announced at the .Net Developers Conference
• The language was renamed C#

Data Types, Variables, and Values

• C# mandates that every variable and constant must have a defined type before use
• Every expression is required to evaluate to a value
• Methods or functions need to have a return value

NET Framework Library

• Contains a large selection of different data type categories
• The typical C# program utilizes data types from the class library
• User-defined types that revolve around concepts specific to the problem domain are also used

Declaring Variables

• Declaring variables requires specifying three elements e.g. data type, name
• Several types of variables and constants exist in C#, including ones for integers, real numbers and characters
• Variables and constants must be declared before use to reserve space
• The name of the variable should adhere to naming conventions
• The type of variable must be from the data types in the table
• Assigning an initial value to a variable is optional

Numerical Data Types

• Numeric data types stay constant and are made up of numbers with minimum and maximum limits
• The limits are based on the type of processor being used

Integer Number Data Types

• Integer Numbers can be positive, negative or zero, subject to these conditions
• They cannot contain decimal points
• Negative numbers need to be prepended with a minus sign (-)
• It can not contain any special symbol, or alphabetical letter

Real Numbers Data Types

• Real numbers carry decimal values
• Should also use any character or symbol or the ‘-‘ sign

General Declaration Format for Variables

• Syntax includes: DataType variable_list [=value]
• Variable_Type Variable_Name = Variable_Value

Variable Declaration Examples

• String declaration: string username;
• String assignment: username="";
• Double percentage declaration double percent=0;
• Percentage assignment: percent=0.35;
• Declaring multiple variables of the same type: int X,Y,Z;
• Declaring multiple doulbe variables: double i,j;

Alternate Declaration Examples

• You can define more than one variable of the same type without repeating the name in the same expression
• Declaring 3 int variables on one line: int X=10,Y,Z=120;
• Declaring a double variable on one line: double i=0.5,j;
• You can break the statement into multiple lines if the semi colon is used

Declaring String Values

• Assigning a value to a string string S ="My name is Aly";
• An error will trigger is you attempt to break a string expression into multiple lines
• To combat this the @ symbol can be used: @“My name is Aly”

Defining Variables using var

• The var keyword specifies that the compiler should infer the type from the assigned value
• It does not mean the variable is a variant
• The data assigned will determine what storage is assigned

Reading data with readline

• Used to assign variables to input data via input units
• var1= Console.ReadLine();
• var1 is the variable that will be kept in memory
• Command line is used to extract user input, store and display

Parsing

• C# offers a lot of functionality used to covert between different data types
• int.Parse Used to convert to Integer
• single.Parse Used to convert to single
• bool.Parse Used to convert to a boolean value: true or false
• char.Parse Used to convert data types to characters

Using Parse

• Specify the type of data you want converted by calling it before Parse and adding parenthesis e.g., Parse()
• strNumber = Console.ReadLine();
• Number = int.Parse(strNumber);
• Can be shortened to one line with: int Number = int.Parse(Console.ReadLine());

Conversion Real World Examples

• String x1 = console.readline(); (No Conversion) Reads a string of characters to variable x1
• Int x2 = int.parse(console.readline()); (Integer Conversion) Reads a string of characters to variable x2 and automatically converts them ints
• double x3 = double.parse(console.readline()); (Double Conversion) Reads a string of characters to variable x3 and automatically converts them doubles to x3 to x3
• bool x4 = bool.parse(console.readline()); Converts text to boolean variable x4 to “true” or “false”
• Char x5 = char.parse(console.readline()) converts text to single characters

Converting Equations to Code

• Compilers can not directly write algebraic equations
• Instead the equations need to be represented in a format that the machine understands
• It is important to write the code out as accurately as possible otherwise the final result may be wrong

Rules for Equations in Code

• Using the designated operators +, -, *, /, ^
• A parenthesis is needed around the operation in the numerator or denominator of an expression

Example Equation

• X=5*A*B^2/(8-A^2)+(A+B)/(3*B^2)
• When there is a numerator with addition/subtractions, and one multiplying on the denominator, use Parenthesis
• Remember “PEMDAS”
• Exponents can be performed using either ^ or Math.Pow

Order of Operators

• Expressions are evaluated based on this order.
• PEMDAS describes the order of precedence for operators: Parenthesis, Exponents, Multiplication, Division, Addition, Subtraction.

Data Types

• String is descriptive data consisting of adjacent Symbols

• Boolean can assign a truth value and can be coded to true or false

• Character Can store information of any code

Expressions

• Used to represent ideas
• The expression can be a constant, variable, or a linked collection

Arithmetic expressions

• Returns calculation of quantitative information
• Sample X*((5+A)/2*3-B)

Logical Expression

• Made using an expression of True, or False

Arithmetic Operators

• Addition: var1=var2+var3
• subtraction: var1=var2-var3
• multiplication: var1=var2*var3
• division: var1=var2/var3
• Modulus: var1=var2%var3

Increment and Decrement Operators

• They increase by the increment of the variable they are applied to

Comparison Operators

• Equal: var1==var2==var3 returns TRUE if Both variances are the same
• Not Equal-returns. Returns TRUE if Not equal
• Less Than: return TRUE If the condition is met
• Greater Than: Returns TRUE. If the condition is met
• Lese/Equal: Returns. If the condition is met
• Great/Equal; Returns. If the condition is met

Logical Operators

• Logical AND: returns TRUE. If the condition is met
• Logical Or: Either is correct as long as at least 1 value is correct
• Logical Non Does not factor in if there is a truth value

Assignment Statement

• Means transferring a property to a variable. Following the pattern: Variable = Expression

MessageBox

• Most programs in #C used dialog forms to direct the output
• The structure contains an item called MessageBox to open the dialog box, in System.Windows.Forms