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;




The main program is contained in a

function (method) called Main





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;


Console.WriteLine("That's correct"); }

Randomly pick a number between

1 - 100





Repeat as long asg != answer





Print a string, then read an integer and

store it in the variable g





Compare g and answer, then

display the hint





Tell the user that the answer is

correct

Dissect The Program: Outer

Blockusing System;




Indicate that this program will use functions from

standard library





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;


First Program

Every statement ends with a ; (semi-colon)

using System;


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;


First Program

Calculate the result and store it

in s

using System;


First Program

Output Statements

using System;


First Program

Input Statement reads user input as

a string

using System;


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 { }



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.



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


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.")


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()


executed


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); }


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

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