Introduction to C# 01204111 Computer and Programming.
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Transcript of Introduction to C# 01204111 Computer and Programming.
Introduction to C#
01204111 Computer and Programming
Agenda
• Why two languages?• Differences between Python
and C#• C# overview• Event-driven programming
Why Two Languages?
• There exist many languages which are quite different from each other
• Python is easy for beginners, but its flexibility makes it different from other languages you will likely use
• The two languages were carefully chosen so that they have distinct syntax– So you will see and learn various
programming styles
Our First C# Programusing System;
class Program{ public static void Main(string[] args) { Random r = new Random(); int answer = 1 + (r.Next() % 100); int g;
do { Console.Write("Guess a number: "); g = int.Parse(Console.ReadLine()); if(g > answer) Console.WriteLine("Too large"); else if(g < answer) Console.WriteLine("Too small"); } while(g != answer);
Console.WriteLine("That's correct"); }}
What does this program
do?
Dissect The Programusing System;
class Program{ public static void Main(string[] args) { Random r = new Random(); int answer = 1 + (r.Next() % 100); int g;
do { Console.Write("Guess a number: "); g = int.Parse(Console.ReadLine()); if(g > answer) Console.WriteLine("Too large"); else if(g < answer) Console.WriteLine("Too small"); } while(g != answer);
Console.WriteLine("That's correct"); }}
The main program is contained in a
function (method) called Main
Dissect The Programusing System;
class Program{ public static void Main(string[] args) { Random r = new Random(); int answer = 1 + (r.Next() % 100); int g;
do { Console.Write("Guess a number: "); g = int.Parse(Console.ReadLine()); if(g > answer) Console.WriteLine("Too large"); else if(g < answer) Console.WriteLine("Too small"); } while(g != answer);
Console.WriteLine("That's correct"); }}
A pair of braces { } are used to specify a block
of code
Dissect The Method Main public static void Main(string[] ar
gs) { Random r = new Random(); int answer = 1 + (r.Next() % 100); int g;
do { Console.Write("Guess a number: "); g = int.Parse(Console.ReadLine()); if(g > answer) Console.WriteLine("Too large"); else if(g < answer) Console.WriteLine("Too small"); } while(g != answer);
Console.WriteLine("That's correct"); }
Randomly pick a number between
1 - 100
Dissect The Method Main public static void Main(string[] ar
gs) { Random r = new Random(); int answer = 1 + (r.Next() % 100); int g;
do { Console.Write("Guess a number: "); g = int.Parse(Console.ReadLine()); if(g > answer) Console.WriteLine("Too large"); else if(g < answer) Console.WriteLine("Too small"); } while(g != answer);
Console.WriteLine("That's correct"); }
Repeat as long asg != answer
Dissect The Method Main public static void Main(string[] ar
gs) { Random r = new Random(); int answer = 1 + (r.Next() % 100); int g;
do { Console.Write("Guess a number: "); g = int.Parse(Console.ReadLine()); if(g > answer) Console.WriteLine("Too large"); else if(g < answer) Console.WriteLine("Too small"); } while(g != answer);
Console.WriteLine("That's correct"); }
Print a string, then read an integer and
store it in the variable g
Dissect The Method Main public static void Main(string[] ar
gs) { Random r = new Random(); int answer = 1 + (r.Next() % 100); int g;
do { Console.Write("Guess a number: "); g = int.Parse(Console.ReadLine()); if(g > answer) Console.WriteLine("Too large"); else if(g < answer) Console.WriteLine("Too small"); } while(g != answer);
Console.WriteLine("That's correct"); }
Compare g and answer, then
display the hint
Dissect The Method Main public static void Main(string[] ar
gs) { Random r = new Random(); int answer = 1 + (r.Next() % 100); int g;
do { Console.Write("Guess a number: "); g = int.Parse(Console.ReadLine()); if(g > answer) Console.WriteLine("Too large"); else if(g < answer) Console.WriteLine("Too small"); } while(g != answer);
Console.WriteLine("That's correct"); }
Tell the user that the answer is
correct
Dissect The Program: Outer
Blockusing System;
class Program{ public static void Main(string[] args) { Random r = new Random(); int answer = 1 + (r.Next() % 100); int g;
do { Console.Write("Guess a number: "); g = int.Parse(Console.ReadLine()); if(g > answer) Console.WriteLine("Too large"); else if(g < answer) Console.WriteLine("Too small"); } while(g != answer);
Console.WriteLine("That's correct"); }}
Indicate that this program will use functions from
standard library
Dissect The Programusing System;
class Program{ public static void Main(string[] args) { Random r = new Random(); int answer = 1 + (r.Next() % 100); int g;
do { Console.Write("Guess a number: "); g = int.Parse(Console.ReadLine()); if(g > answer) Console.WriteLine("Too large"); else if(g < answer) Console.WriteLine("Too small"); } while(g != answer);
Console.WriteLine("That's correct"); }}
Every method must reside in a
class
Coding in Different Languages
Hello,May I have a
fried rice, and water please?
Bonjour, Puis-je avoir un riz frit, et de l'eau s'il vous plaît?
Solving the same task using a different language usually has on the same flow of thought and steps. The only differences are syntax and wording.
C# Program Structure
using System;
namespace Sample{ class Program { static void Main() { Console.WriteLine("Hello, world"); } }}
C# uses braces { } to specify scopes of things
Program on the left contains1.namespace Sample2.class Program3.method Main
C# Program Structure
using System;
namespace Sample{ class Program { static void Main() { Console.WriteLine("Hello, world"); } }}
C# statements are contained in a bigger structure
Statements are inside a method
Methods are inside a class
Classes may or may not be inside a namespace
The Universe of C# Programs
Namespace System
Class ConsoleWriteLine
ReadLine
Write
Class Integer
Parse
ToString
Class RandomNext
Class Float
Namespace Sample
(Our own namespace)
ClassProgram
Main
Class X
Class Y …
• The statement using System; at the beginning of the program indicates that our program will use the System namespace as our own namespace
using System
Namespace Sample
(Our own namespace)
ClassProgram
Main
Namespace System
Class ConsoleWriteLine
ReadLine
Write
Class Integer
Parse
ToString
Class RandomNext
Class Float
using System;
namespace Sample{ class Program { …… }}
The Main Program: Method Main
using System;
namespace Sample{ class Program { static void Main() {
} }}
The program always starts at the method Main
We will write our main program here.
Just Ignore Them (For Now)
• What are classes?• What is this "static void"
thing?We will not answer these questions at the moment. For the time being, just use them
as shown. You will know when the time comes…
We will not answer these questions at the moment. For the time being, just use them
as shown. You will know when the time comes…
Example: Distance Calculation
• A still object starts moving in a straight line with the acceleration of a m/s2 for t seconds.
• How far is it from its starting point?
Developing C# Programs
• We will use a tool called Integrated Development Environment, or IDE–Allows code editing, testing, and debugging
–Similar to WingIDE
• We will first start with text-only programs–Also known as console applications
Start Writing Program
• The IDE we will be using is call SharpDevelop.• Microsoft Visual Studio Express can also be used.
Create a Solution • A program is called
a solution• Choose New
Solution– Choose Console
Application– Enter solution name
• Once done, stub code will be created
IDE Window• Code editor is
located at the center of the window
• Other parts show properties and structure of the program
using System;
namespace mecha1{ class Program { public static void Main(string[] args) { double a, t, s; Console.Write("Enter a: "); a = double.Parse(Console.ReadLine()); Console.Write("Enter t: "); t = double.Parse(Console.ReadLine()); s = a*t*t/2.0; Console.WriteLine("Distance = {0}", s); } }}
First Program
Identify similarities and
differences, compared to a
Python program
using System;
namespace mecha1{ class Program { public static void Main(string[] args) { double a, t, s; Console.Write("Enter a: "); a = double.Parse(Console.ReadLine()); Console.Write("Enter t: "); t = double.Parse(Console.ReadLine()); s = a*t*t/2.0; Console.WriteLine("Distance = {0}", s); } }}
First Program
Every statement ends with a ; (semi-colon)
using System;
namespace mecha1{ class Program { public static void Main(string[] args) { double a, t, s; Console.Write("Enter a: "); a = double.Parse(Console.ReadLine()); Console.Write("Enter t: "); t = double.Parse(Console.ReadLine()); s = a*t*t/2.0; Console.WriteLine("Distance = {0}", s); } }}
First Program
Variables must be declared with
proper data types before used.
Here, double is a data type for storing a real
number.
using System;
namespace mecha1{ class Program { public static void Main(string[] args) { double a, t, s; Console.Write("Enter a: "); a = double.Parse(Console.ReadLine()); Console.Write("Enter t: "); t = double.Parse(Console.ReadLine()); s = a*t*t/2.0; Console.WriteLine("Distance = {0}", s); } }}
First Program
Calculate the result and store it
in s
using System;
namespace mecha1{ class Program { public static void Main(string[] args) { double a, t, s; Console.Write("Enter a: "); a = double.Parse(Console.ReadLine()); Console.Write("Enter t: "); t = double.Parse(Console.ReadLine()); s = a*t*t/2.0; Console.WriteLine("Distance = {0}", s); } }}
First Program
Output Statements
using System;
namespace mecha1{ class Program { public static void Main(string[] args) { double a, t, s; Console.Write("Enter a: "); a = double.Parse(Console.ReadLine()); Console.Write("Enter t: "); t = double.Parse(Console.ReadLine()); s = a*t*t/2.0; Console.WriteLine("Distance = {0}", s); } }}
First Program
Input Statement reads user input as
a string
using System;
namespace mecha1{ class Program { public static void Main(string[] args) { double a, t, s; Console.Write("Enter a: "); a = double.Parse(Console.ReadLine()); Console.Write("Enter t: "); t = double.Parse(Console.ReadLine()); s = a*t*t/2.0; Console.WriteLine("Distance = {0}", s); } }}
First Program
Convert string into real number
(double)
Difference: Use { } To Indicate Blocks
//// Other parts are omitted//static void Main(){ int n = int.Parse(Console.ReadLine()); int i = 1; while(i <= n) { if(i % 3 == 0) { Console.WriteLine(i); } } }
def main(): n = int(input()) i = 1 while i <= n: if i % 3 == 0: print(i)
Python C#
Python uses indentation
C# uses { }
Difference: Use { } To Indicate Blocks
//// Other parts are omitted//static void Main(){ int n = int.Parse(Console.ReadLine()); int i = 1; while(i <= n) { if(i % 3 == 0) { Console.WriteLine(i); } } }
C#//// Other parts are omitted//static void Main(){int n = int.Parse(Console.ReadLine());int i = 1;while(i <= n) {if(i % 3 == 0){Console.WriteLine(i); }} }
C#
Indentations have no effect on program logic. They are used for improving readability.
Difference: Use { } To Indicate Blocks
//// Other parts are omitted//static void Main(){ int n = int.Parse(Console.ReadLine()); int i = 1; while(i <= n) { if(i % 3 == 0) { Console.WriteLine(i); } } }
C#//// Other parts are omitted//static void Main(){ int n = int.Parse(Console.ReadLine()); int i = 1; while(i <= n) if(i % 3 == 0) Console.WriteLine(i); }
C#
For control statements such as while or if, omitting { } means the following block contains only one statement.
Difference: Variable Declaration
//// Other parts are omitted//static void Main(){ int n = int.Parse(Console.ReadLine()); int total = 0; int i = 0; int x; while(i < n) { x = int.Parse(Console.ReadLine()); total += x; i += 1; } }
n = int(input())total = 0i = 0while i < n: x = int(input()) total += x i += 1print(total)
Python C#
Declaring Variables• Syntax:
<Data type> <Variable name>;<Data type> <Var name>, <Var name>, …;
• Ex:
• Initial values can be given right awayEx:
double area;int radius, counter;bool isOkay;
double area;int radius, counter;bool isOkay;
int k = 200;bool done = false;int k = 200;bool done = false;
Multiple vars.
Single var
Basic Data Types in C#
Type Size Description Rangebool 1 byte Store truth value true / false char 1 byte Store one character character code 0 – 255byte 1 byte Store positive integer 0 – 255short 2 byte Store integer -32,768 -- 32,767int 4 byte Store integer -2.1 x 109 -- 2.1 x 109 long 8 byte Store integer -9.2 x 1018 -- 9.2 x 1018
double 16 byte Store real number ± 5.0x10-324 -- ± 1.7x10308
string N/A Store sequence of characters
N/A
Computing Summation
• Write a program that takes a list of positive integers from user until -1 is entered, then displays the sum of all the numbers in the list
Summation: Pythontotal = 0num = 0while num != -1: num = int(input()) if num != -1: total += numprint(total)
total = 0num = 0while num != -1: num = int(input()) if num != -1: total += numprint(total)
Summation: C#
• Summation program written in C#static void Main()
{ int total = 0; int num = 0; while(num != -1) { num = int.Parse(Console.ReadLine()); if(num != -1) total += num; } Console.WriteLine(total);}
static void Main(){ int total = 0; int num = 0; while(num != -1) { num = int.Parse(Console.ReadLine()); if(num != -1) total += num; } Console.WriteLine(total);}
total = 0num = 0while num != -1:
num = int(input()) if num != -1: total += num
print(total)
total = 0num = 0while num != -1:
num = int(input()) if num != -1: total += num
print(total)
C# and Python: Difference Summary• Use { } to indicate
blocks• Variables
– Must always be declared with data type specified
– One variable can store one data type
• Usually run faster
• Use indentation for blocks
• Variables– Can be used instantly
– Each variable can store any data type, which can be changed during the program execution
• Usually run slower
C# Python
Cost and Benefit
• We lose many flexibilities in C#, but more errors can be found much earlier
Erroneous Python Program
x = int(input("Enter price: "))if x <= 10: print("You have to pay",x,"baht.")else: print("You have to pay",y*0.95,"baht.")
Do you spot the error?Do you spot the error?Enter price: 7You have to pay 7 baht.Enter price: 7You have to pay 7 baht.
Enter price: 20Traceback (most recent call last): File "<string>", line 5, in <fragment>builtins.NameError: name 'y' is not defined
Enter price: 20Traceback (most recent call last): File "<string>", line 5, in <fragment>builtins.NameError: name 'y' is not defined
We will know only when the erroneous line gets
executed
We will know only when the erroneous line gets
executed
Erroneous C# Program
public static void Main(string[] args) { double x; Console.Write("Enter price: "); x = double.Parse(Console.ReadLine());
if(x <= 10) Console.WriteLine("You have to pay {0} baht.", x); else Console.WriteLine("You have to pay {0} baht.", y*0.95); }
Do you spot the error?Do you spot the error?
This C# program will not compile. The compiler will reportThe name 'y' does not exist in the current context.
Erroneous Python Program
x = input("Enter price: ")if x <= 10: print("You have to pay",x,"baht.")else: print("You have to pay",x*0.95,"baht.")
Do you spot the error?Do you spot the error?
There is a problem because we try to compare an integer with a stringThere is a problem because we try to compare an integer with a string
Traceback (most recent call last): File "<string>", line 2, in <fragment>builtins.TypeError: unorderable types: str() <= int()
Traceback (most recent call last): File "<string>", line 2, in <fragment>builtins.TypeError: unorderable types: str() <= int()
We will know only when the erroneous line gets
executed
We will know only when the erroneous line gets
executed
Erroneous C# Program
public static void Main(string[] args) { String x; Console.Write("Enter price: "); x = Console.ReadLine();
if(x <= 10) Console.WriteLine("You have to pay {0} baht.", x); else Console.WriteLine("You have to pay {0} baht.", x*0.95); }
Do you spot the error?Do you spot the error?
This C# program won't compile. Two errors will be reported1. Operator '<=' cannot be applied to operands of
type 'string' and 'int'.2. Operator '*' cannot be applied to operands of
type 'string' and 'double'
Choosing a Language
StrictUnintentional errors
caught before the program starts
Longer programs cause more difficulties
More limitations
StrictUnintentional errors
caught before the program starts
Longer programs cause more difficulties
More limitations
GenerousEasy and faster to
write program, with more flexibility
Errors might be found after the program
startedCan be a problem with
large programs
GenerousEasy and faster to
write program, with more flexibility
Errors might be found after the program
startedCan be a problem with
large programs
Justification of This Course
• This course begins with Python, which is easy for beginners
• The second half uses C#, which has more restrictions, so we write more organized programs
• This is to allow students to understand the programming concept, without being tied to a specific language
Your Choices• There are many
other programming languages
• Most importantly, pick the right tool for the right job
Executing a Program: Review
• We write a program in a high-level language
• But the CPU understands only machine language
• There must be a process of translating what we wrote into something the CPU understands
Executing a C# Program
• C# programs are compiled by a compiler into a form that can be executed by the computer
• However, certain software infrastructure must also be installed in the computer
C# Program C# Compiler Executable Code
Graphic User Interface
• C# development environment provides great convenience for creating applications (programs) that interact with users graphically
• Such applications are said to contain GUI (graphics user interface); they are called GUI applications
• Let's build a simple GUI application
Typical GUI Applications
• Users can interact with the program in many different ways
• Therefore, the sequence of execution is not certain, compared to console applications
Click hereClick hereClick here
Click here
Click here
Edit here
Edit here
Writing a GUI Program (1)
• Consider a program that reads a set of data
• In a GUI program, user may enter values in many different orders
• Coding in sequential style is therefore not suitable in GUI programs
int w = int.Parse(Console.ReadLine());int h = int.Parse(Console.ReadLine());Console.Write("Choose unit: ");string u = Console.ReadLine();Console.Write("Choose background:");string b = Console.ReadLine();
int w = int.Parse(Console.ReadLine());int h = int.Parse(Console.ReadLine());Console.Write("Choose unit: ");string u = Console.ReadLine();Console.Write("Choose background:");string b = Console.ReadLine();
Writing a GUI Program (2)
• As there are various ways user can interact with the program, a piece of code is written to handle each particular event–This is called event-driven
programmingWhat to do when this
button is clicked?
What to do when this button is clicked?
What to do when this button is clicked?
What to do when this value changes?
What to do when this value changes?
Event-Driven Programming
• We will write a program that responds to an event
• When an event of interest occurs, the corresponding part of program will be executed
• Consider the following programIf this button is clicked" Change the text above to "Sawaddee"
If this button is clicked" Change the text above to "Sawaddee"
The program responds to the button click as follows:
Create a Solution
• Choose New solution
• Choose Windows Application
• Enter the solution's name
User Interface Design
• Once we create a Windows application–We will be able to click on the Design tab to design our window layout for the user interface
Click "Design"
Click "Tools"
Hello, worldButtons and labels, available in the Tools tab, can be placed on the window. There properties can also be modified via the Properties box.
Buttons and labels, available in the Tools tab, can be placed on the window. There properties can also be modified via the Properties box.
Caution: do not double-click. If you do and the code window shows up, click Design to go back to the design screen.
Caution: do not double-click. If you do and the code window shows up, click Design to go back to the design screen.
Objects on the Window
• We have already placed two objects• The IDE sets default names to the
objects as follows:
• These names can be changed, but we will stick to them for now
label1
button1
Objects and Their Properties
• Each object on the window has editable properties.
• E.g., the button1 object has some properties shown in the right
Properties• The Properties tab allows us to
adjust text, text font, color, etc.
Change the font by editing Font propertyChange the text by editing the Text
property
Writing the Program• We will write the program so that
the text "Hello, world" is displayed at label1 when the button button1 is clicked–In the design window, double click button1
–The design window will disappear. The IDE will display code that allows you to edit
Writing the Program
We will write our program in this Button1Click method
Handling the Event
• We write an event-handling method as follows:void Button1Click(object sender, EventArgs e)
{ label1.Text = "Sawaddee";}
void Button1Click(object sender, EventArgs e){ label1.Text = "Sawaddee";}
Change the text on label1 to "Sawaddee"
ClickClick
CallsButton1Click
CallsButton1Click
Binding Event to Method
• We can bind any method to the Click event from the Properties box
• However, by double clicking an object, the IDE will automatically create a new method to handle the object's default event.
Adding Numbers
• Let us write a program that takes two integers, then displays their sum
• We start with the user interface design, which consists of a button, two text boxes, and a label
User Interface Design
• New Solution, choose Windows Application
• Place objects on the design window as shown label
button
text box
text box
Object Names
• IDE will automatically assign names for referring to those objects as shown
label1
button1
textBox1
textBox2
Choose Better Names
• The default names do not make a lot of sense. That will make our program difficult to read
• So we replace them with better ones
resultLabel
addButton
xTextBox
yTextBox
Watch out the lower/upper casesWatch out the lower/upper cases
Changing Names
Change the name by editing the Name property.
These names are used to refer to the objects and their properties in
our program.
Handling Button Click
• In the design window, double click the button, then enter the following methodvoid AddButtonClick(object sender, EventArgs e)
{ int x = int.Parse(xTextBox.Text); int y = int.Parse(yTextBox.Text); int result = x + y; resultLabel.Text = result.ToString();}
void AddButtonClick(object sender, EventArgs e){ int x = int.Parse(xTextBox.Text); int y = int.Parse(yTextBox.Text); int result = x + y; resultLabel.Text = result.ToString();}
Thinking Corner
• Add another button to multiply the two numbers