DCIT 318
PROGRAMMING II
Session 1 – Introduction to C#
and .NET framework
Lecturer: Mr. Paul Ammah, CSD
Contact Information: pammah@ug.edu.gh
Department of Computer Science
School of Physical and Mathematical Sciences
2024/2025
Introduction to .NET
• The .NET Framework is one of the most popular widely used
integrated software development environments today.
• .NET Framework allows the integration of codes written in
different programming languages.
• Earlier each language required different execution
environments.
• But with the introduction of .NET framework this problem was
solved.
• .NET Framework provides programmers a single platform to
develop Windows and Web applications in various
programming languages, such as Visual Basic(VB) and Visual
C#
Slide 2
Generations of .NET Framework
• .NET Framework 1.0
• .NET Framework 1.1
• .NET Framework 2.0
• .NET Framework 3.0
• .NET Framework 3.5
• .NET Framework 4.0(release year-2010)
• .NET Framework 4.5(release year-2012)
• .NET Framework 4.6(release year-2015)
• .NET Framework 4.7(release year-2017)
• ….
• .NET Framework 6.0
• .NET Framework 7.0
Slide 3
Benefits of .NET Framework
• Consistent Programming Model: By using this model different tasks such
as Database Connectivity, Reading from and Writing to files is performed.
• Language Interoperability: Piece of code written in one language can be
used in another language.
• Automatic Management of Resources: Garbage Collection(Part of CLR)
performs the allocation and de allocation of all the resources such as files,
memory and database connections. Programmer does not need to provide
code for memory management tasks.
• Ease of Deployment: Applications coded under .NET Framework can be
easily deployed(installed on computer) because deployment is done in the
form of assemblies which are the single , logical deployment unit and
hence registries does not need to store information about components and
applications.
Slide 4
Core Components of .NET Framework
• Common Language Runtime
• Common Type System
• Common Language Specification
• .NET Framework Class Library(Base Class Library)
• Windows Forms
• ASP.NET and ASP.NET Ajax
• ADO.NET
• WPF and WCF
Slide 5
.NET Architecture
Slide 6
.NET Framework
ASP.NET
ASP.NET Windows
WindowsForms
Forms
Web Services Web Forms Controls Drawing
ASP.NET Application Services Windows Application Services
Framework
FrameworkClass
ClassLibrary
Library
ADO.NET XML Threading IO
Network Security Diagnostics Etc.
Common
CommonLanguage
LanguageRuntime
Runtime
Memory Management Common Type System Lifecycle Monitoring
Slide 7
Common Language Runtime
• A Common Language Runtime (CLR) provides essential runtime
services such as automatic memory management and exception
handling.
• The CLR is at the core of the .NET platform - the execution
engine. A unifying framework for designing, developing,
deploying, and executing distributed components and
applications.
• Loads and runs code written in any runtime-aware programming
language
• Manages memory, thread execution, type safety verification and
garbage collection.
• Performs compilation (Just In-time Compiler)
• Makes use of a new common type system capable of expressing
the semantics of most modern programming languages.
• The common type system defines a standard set of types and
rules for creating new types. Slide 8
MSIL and JIT Compilation
• Source code is compiled into MSIL (Microsoft Intermediate Language).
Similar to Java bytecode.
• MSIL allows for runtime type-safety and security, as well as portable
execution platforms (all Windows).
• MSIL code cannot play tricks with pointers or illegal type conversions.
• The MSIL architecture results in apps that run in one address space - thus
much less OS overhead.
• Compilers also produce “metadata”:
– Definitions of each type in your code.
– Signatures of each type’s members.
– Members that your code references.
– Other runtime data for the CLR.
• Metadata along with the MSIL enables code to be self-describing - no need
for separate type libraries, IDL, or registry entries.
• When code is executed by the CLR, a JIT compilation step occurs.
• Code is compiled method-by-method to native machine code.
Slide 9
Packaging: Modules, Types,
Assemblies, and the Manifest
Assembly
Assembly
Manifest
Module
Metadata
MSIL
Type Type Type
Slide 10
Packaging: Modules, Types,
Assemblies, and the Manifest
• A module refers to a binary, such as an EXE or DLL.
• Modules contain definitions of types, such as classes, interfaces,
structures, and enumerations.
• An assembly contains a manifest, which is a catalog of
component metadata containing:
– Assembly name.
– Version (major, minor, revision, build).
– Assembly file list - all files contained in the assembly.
– Type references - mapping the managed types included in the assembly
with the files that contain them.
– Scope - private or shared.
– Referenced assemblies.
• No MSIL code can be executed unless there is a manifest
associated with it.
Slide 11
.NET Tools
Microsoft Visual Studio .NET and Microsoft .NET
Framework supplies complete solution for
developers to build, deploy and run XML services
Visual Studio .NET is the next generation of
Microsoft’s popular multi-language development
tool built especially for .NET
Enhances existing languages like Visual Basic
with new OO features
Introduces C#
Slide 12
Microsoft C#
• A modern, object-oriented programming language
built from the ground up to exploit the power of
XML-based Web services on the .NET platform.
• The main design goal of C# was simplicity rather than
pure power.
• Features of C#
Simplicity Type Safety
Consistency Version Control
Modernity Compatibility
Object Orientation Flexibility
Slide 13
C# Language
• C# is type-safe object-oriented language
• Enables developers to build a variety of secure and
robust applications
• Very similar in syntax to C, C++, and Java.
• Syntax is highly expressive.
• Key features: nullable value type, enumerations,
delegates, lambda expressions, and direct memory
access
Slide 14
Compile-time and Run-time Relationships
of C#
Slide 15
C# Program Structure
• Namespaces
– Contain types and other namespaces
• Type declarations
– Classes, structs, interfaces, enums,
and delegates
• Members
– Constants, fields, methods, properties, indexers, events,
operators, constructors, destructors
• Organization
– No header files, code written “in-line”
– No declaration order dependence
Slide 16
Type System
• Value types
– Directly contain data
– Cannot be null
• Reference types
– Contain references to objects
– May be null
int i = 123;
string s = "Hello world";
Slide 17
Type System
• Value types
– Primitives int i;
– Enums enum State { Off, On }
– Structs struct Point { int x, y; }
• Reference types
– Classes class Foo: Bar, IFoo {...}
– Interfaces interface IFoo: IBar
{...}
– Arrays string[] a = new string[10];
– Delegates delegate void Empty();
Slide 18
Predefined Types
• C# predefined types
– Reference object, string
– Signed sbyte, short, int, long
– Unsigned byte, ushort, uint, ulong
– Character char
– Floating-point float, double, decimal
– Logical bool
• Predefined types are simply aliases for system-
provided types
– For example, int == System.Int32
Slide 19
Classes
• Single inheritance
• Multiple interface implementation
• Class members
– Constants, fields, methods, properties, indexers, events,
operators, constructors, destructors
– Static and instance members
– Nested types
• Member access
– public, protected, internal, private
Slide 20
Structs
• Like classes, except
– Stored in-line, not heap allocated
– Assignment copies data, not reference
– No inheritance
• Ideal for light weight objects
– Complex, point, rectangle, color
– int, float, double, etc., are all structs
• Benefits
– No heap allocation, less GC pressure
– More efficient use of memory
Slide 21
Decision Statements
• If..else if..else
• Tenary Operators (?:)
• Switch Statements
Slide 22
The if statement
void DisplayCharacter(char ch)
{
if (char.IsUpper(ch))
{
Console.WriteLine($"An uppercase letter: {ch}");
}
else if (char.IsLower(ch))
{
Console.WriteLine($"A lowercase letter: {ch}");
}
else if (char.IsDigit(ch))
{
Console.WriteLine($"A digit: {ch}");
}
else
{
Console.WriteLine($"Not alphanumeric character: {ch}");
}
}
Slide 23
Switch Statements
void DisplayMeasurement(double measurement)
{
switch (measurement)
{
case < 0.0:
Console.WriteLine($"Measured value is {measurement}; too low.");
break;
case > 15.0:
Console.WriteLine($"Measured value is {measurement}; too high.");
break;
case double.NaN:
Console.WriteLine("Failed measurement.");
break;
default:
Console.WriteLine($"Measured value is {measurement}.");
break;
}
}
Slide 24
Ternary Operator
• The conditional operator ?:, also known as the
ternary conditional operator, evaluates a Boolean
expression and returns the result of one of the two
expressions, depending on whether the Boolean
expression evaluates to true or false
string weatherDisplayString = tempInCelsius < 20.0 ? "Cold." :
"Perfect!";
Slide 25
Iteration statements
• while loop
• For loop
• Foreach loop
• Do loop
Slide 26
The for statement
• The for statement executes a statement or a block of
statements while a specified Boolean expression
evaluates to true
for (int i = 0; i < 3; i++)
{
Console.Write(i);
}
Slide 27
The foreach statement
• The foreach statement executes a statement or a block of statements for
each element in an instance of the type that implements the
System.Collections.IEnumerable or
System.Collections.Generic.IEnumerable<T> interface
var fibNumbers = new List<int> { 0, 1, 1, 2, 3, 5};
foreach (int element in fibNumbers)
{
Console.Write($"{element} ");
}
Slide 28
The while statement
• The while statement executes a statement or a block
of statements while a specified Boolean expression
evaluates to true
int n = 0;
while (n < 5)
{
Console.Write(n);
n++;
}
Slide 29
The do statement
• The do statement executes a statement or a block of statements while a
specified Boolean expression evaluates to true.
• Because that expression is evaluated after each execution of the loop, a do
loop executes one or more times.
int n = 0;
do
{
Console.Write(n);
n++;
} while (n < 5);
Slide 30
C# Special Characters
• Special characters are predefined, contextual
characters that modify the program element (a literal
string, an identifier, or an attribute name) to which
they are prepended.
• C# supports the following special characters:
– @, the verbatim identifier character.
– $, the interpolated string character.
Slide 31
Verbatim text - @ in variables, attributes, and string literals
• The @ special character serves as a verbatim
identifier.
• You use it in the following ways:
– To indicate that a string literal is to be interpreted verbatim
– To use C# keywords as identifiers
– To enable the compiler to distinguish between attributes in
cases of a naming conflict
Slide 32
Verbatim String Literal
string filename1 = @"c:\documents\files\u0066.txt";
string filename2 = "c:\\documents\\files\\u0066.txt";
Console.WriteLine(filename1);
Console.WriteLine(filename2);
// The example displays the following output:
-> c:\documents\files\u0066.txt
-> c:\documents\files\u0066.txt
Slide 33
C# keywords as identifiers
• The @ character prefixes a code element that the compiler is to interpret as
an identifier rather than a C# keyword
string[] @for = { "John", "James", "Joan", "Jamie" };
for (int ctr = 0; ctr < @for.Length; ctr++)
{
Console.WriteLine($"Here is your gift, {@for[ctr]}!");
}
// The example displays the following output:
// Here is your gift, John!
// Here is your gift, James!
// Here is your gift, Joan!
// Here is your gift, Jamie!
Slide 34
String interpolation using $
• The $ special character identifies a string literal as an
interpolated string.
• An interpolated string is a string literal that might
contain interpolation expressions
• When an interpolated string is resolved to a result
string, items with interpolation expressions are
replaced by the string representations of the
expression results.
• String interpolation provides a more readable,
convenient syntax to format strings.
Slide 35
String interpolation using $
string name = "Mark";
var date = DateTime.Now;
// Composite formatting:
Console.WriteLine("Hello, {0}! Today is {1}, it's
{2:HH:mm} now.", name, date.DayOfWeek, date);
// String interpolation:
Console.WriteLine(
$"Hello, {name}! Today is {date.DayOfWeek}, it’s
{date:HH:mm} now.”
);
Slide 36
Raw string literal text - """
• A raw string literal starts and ends with a minimum of three
double quote (") characters
• Raw string literals can span multiple lines
var xml = """
<element attr="content">
<body>
</body>
</element>
""";
Slide 37
