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Computer and Programming

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1 01204111 Computer and Programming
Introduction to C# Computer and Programming

2 Agenda Why two languages? Differences between Python and C#
C# overview Event-driven programming

3 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

4 What does this program do?
Our First C# Program What does this program do? using 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");   } }

5 The main program is contained in a function (method) called Main
Dissect The Program using 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

6 A pair of braces { } are used to specify a block of code
Dissect The Program using 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

7 Dissect The Method Main
  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");   } Randomly pick a number between

8 Dissect The Method Main
  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");   } Repeat as long as g != answer

9 Dissect The Method Main
  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");   } Print a string, then read an integer and store it in the variable g

10 Dissect The Method Main
  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");   } Compare g and answer, then display the hint

11 Dissect The Method Main
  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");   } Tell the user that the answer is correct

12 Dissect The Program: Outer Block
using 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

13 Every method must reside in a class
Dissect The Program using 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

14 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.

15 C# Program Structure C# uses braces { } to specify scopes of things
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 contains namespace Sample class Program method Main

16 C# Program Structure C# statements are contained in a bigger 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

17 The Universe of C# Programs
Namespace System Namespace Sample (Our own namespace) Class X Class Console WriteLine Class Float Write ReadLine Class Program Class Integer Class Random Parse Main Next ToString Class Y

18 using System 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 { class Program …… } Namespace System Namespace Sample (Our own namespace) Class Program Main Class Console WriteLine ReadLine Write Class Integer Parse ToString Class Random Next Class Float

19 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.

20 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…

21 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?

22 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

23 Start Writing Program The IDE we will be using is call SharpDevelop.
Microsoft Visual Studio Express can also be used.

24 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

25 IDE Window Code editor is located at the center of the window
Other parts show properties and structure of the program

26 Identify similarities and differences, compared to a Python program
First 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);     }   } } Identify similarities and differences, compared to a Python program

27 Every statement ends with a ;
First 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);     }   } } Every statement ends with a ; (semi-colon)

28 First 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);     }   } } Variables must be declared with proper data types before used. Here, double is a data type for storing a real number.

29 Calculate the result and store it in s
First 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);     }   } } Calculate the result and store it in s

30 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);     }   } } Output Statements

31 Input Statement reads user input as a string
First 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);     }   } } Input Statement reads user input as a string

32 Convert string into real number (double)
First 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);     }   } } Convert string into real number (double)

33 Difference: Use { } To Indicate Blocks
Python C# def main(): n = int(input()) i = 1 while i <= n: if i % 3 == 0: print(i) // // 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); } Python uses indentation C# uses { }

34 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.

35 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.

36 Difference: Variable Declaration
Python C# n = int(input()) total = 0 i = 0 while i < n: x = int(input()) total += x i += 1 print(total) // // 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; }

37 Declaring Variables Syntax: Ex:
<Data type> <Variable name>; <Data type> <Var name>, <Var name>, …; Ex: Initial values can be given right away Ex: Single var Multiple vars. double area; int radius, counter; bool isOkay; int k = 200; bool done = false;

38 Basic Data Types in C# Type Size Description Range bool 1 byte
Store truth value true / false char Store one character character code 0 – 255 byte Store positive integer 0 – 255 short 2 byte Store integer -32, ,767 int 4 byte -2.1 x x 109 long 8 byte -9.2 x x 1018 double 16 byte Store real number ± 5.0x ± 1.7x10308 string N/A Store sequence of characters

39 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

40 Summation: Python total = 0 num = 0 while num != -1:
num = int(input()) if num != -1: total += num print(total)

41 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); total = 0 num = 0 while num != -1: num = int(input()) if num != -1: total += num print(total)

42 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

43 Cost and Benefit We lose many flexibilities in C#, but more errors can be found much earlier

44 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? Enter price: 7 You have to pay 7 baht. We will know only when the erroneous line gets executed Enter price: 20 Traceback (most recent call last): File "<string>", line 5, in <fragment> builtins.NameError: name 'y' is not defined

45 Erroneous C# Program Do you spot the error?
    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? This C# program will not compile. The compiler will report The name 'y' does not exist in the current context.

46 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? There 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() We will know only when the erroneous line gets executed

47 This C# program won't compile. Two errors will be reported
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? This C# program won't compile. Two errors will be reported 1. Operator '<=' cannot be applied to operands of type 'string' and 'int'. 2. Operator '*' cannot be applied to operands of type 'string' and 'double'

48 Choosing a Language Strict Generous
Unintentional errors caught before the program starts Longer programs cause more difficulties More limitations Generous Easy and faster to write program, with more flexibility Errors might be found after the program started Can be a problem with large programs

49 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

50 Your Choices There are many other programming languages
Most importantly, pick the right tool for the right job

51 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

52 Executing a C# Program C# Compiler C# Program Executable Code 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

53 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

54 Typical GUI Applications
Click here Edit here Click here Click here Click here Edit here Click here Users can interact with the program in many different ways Therefore, the sequence of execution is not certain, compared to console applications

55 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();

56 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 programming What 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?

57 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 program The program responds to the button click as follows: If this button is clicked" Change the text above to "Sawaddee"

58 Create a Solution Choose New solution Choose Windows Application
Enter the solution's name

59 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"

60 Hello, world 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.

61 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

62 Objects and Their Properties
Each object on the window has editable properties. E.g., the button1 object has some properties shown in the right

63 Properties The Properties tab allows us to adjust text, text font, color, etc. Change the font by editing Font property Change the text by editing the Text property

64 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

65 We will write our program in this Button1Click method
Writing the Program We will write our program in this Button1Click method

66 Change the text on label1 to "Sawaddee"
Handling the Event We write an event-handling method as follows: void Button1Click(object sender, EventArgs e) {   label1.Text = "Sawaddee"; } Change the text on label1 to "Sawaddee" Calls Button1Click Click

67 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.

68 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

69 User Interface Design New Solution, choose Windows Application
Place objects on the design window as shown text box label text box button

70 Object Names IDE will automatically assign names for referring to those objects as shown textBox1 label1 textBox2 button1

71 Watch out the lower/upper cases
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 xTextBox resultLabel yTextBox addButton Watch out the lower/upper cases

72 Change the name by editing the Name property.
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.

73 Handling Button Click In the design window, double click the button, then enter the following method 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(); }

74 Thinking Corner Add another button to multiply the two numbers


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