no slide title - sabraz...2017/07/04 · the if / else statement• an if-else statement will...

Lesson 04Control Structures I :

Decision MakingMIT 31043, VISUAL PROGRAMMING

By: S. Sabraz NawazSenior Lecturer in MIT

Department of MIT

Faculty of Management and Commerce

South Eastern University of Sri Lanka

Decision Structures

• A control structure is a logical design that

controls the order in which statements execute

• A sequence structure is a set of statements that

execute in the order that they appear

• A decision structure execute statements only

under certain circumstances

o A specific action is performed only if a certain

condition exists

o Also known as a selection structure

By: S. Sabraz Nawaz

A Simple Decision Structure

• The flowchart is a single-alternative decision

structure

• It provides only one alternative path of execution

• In C#, you can use the if statement to write such

structures. A generic format is:

if (expression)

{

Statements;

Statements;

etc.;

}

• The expression is a Boolean expression that can

be evaluated as either true or false

Coldoutside

Wear a coat

True

False

By: S. Sabraz Nawaz

Relational Operators

• A relational operator determines whether a specific

relationship exists between two values

Operator Meaning Expression Meaning

> Greater than x > y Is x greater than y?

< Less than x < y Is x less than y?

>= Greater than or equal to x >= y Is x greater than or equal to y?

<= Less than or equal to x <= y Is x less than or equal to you?

== Equal to x == y Is x equal to y?

!= Not equal to x != y Is x not equal to you?

By: S. Sabraz Nawaz

Examples that use relational operators

By: S. Sabraz NawazSlide 5

strFirstName == "Rapid" // equal to a string literal

yearsTextbox.Text == "" // equal to an empty string

strMessage == String.Empty // equal to an empty string

dblDiscountPercent == 2.3 // equal to a numeric literal

blnIsValid == false // equal to the false value

decCode == decProductCode // equal to another variable

strLastName != "Apps" // not equal to a string literal

dblYears > 0 // greater than a numeric literal

intI < intMonths // less than a variable

dblSubtotal >= 500 // greater than or equal to

// a literal value

intQuantity <= intReorderPoint // less than or equal to

// a variable

BRANCHING


BRANCHING

• Branching is the act of controlling which line of code should

be executed next. The line to jump to is controlled by some

kind of conditional statement. This conditional statement is

based on a comparison between a test value and one or more

possible values using Boolean logic.

• This section describes three branching techniques available in

C#:

o The ternary operator

o The if statement

o The switch statement


The Ternary Operator

• The simplest way to perform a comparison is to use the

ternary (or conditional) operator; this operator works on three

operands.


The if Statement

• The if statement is a far more versatile and useful way to make

decisions. Unlike the ternary operator, if statements don’t have

a result (so you can’t use them in assignments); instead, you

use the statement to conditionally execute other statements.


The if Statement• The simplest use of an if statement is as follows, where <test> is evaluated

(it must evaluate to a Boolean value for the code to compile) and the line of

code that follows the statement is executed if <test> evaluates to true:


if (sales > 50000)

bonus = 500;

if (sales > 50000)

{

bonus = 500;

}

sales > 50000

bonus = 500

True

False

The if / else Statement• An if-else statement will execute

one block of statement if its

Boolean expression is true or

another block if its Boolean

expression is false It has two

parts: an if clause and an else

clause

• You can also specify additional

code using the else statement in

combination with an if statement.

This statement is executed if

<test> evaluates to false:


Both sections of code can span multiple

lines using blocks in braces:

Example of if-else Statement

temp >40

display “hot”display “cold”

TrueFalse

if (temp > 40)

{

MessageBox.Show(“hot”);

}

else

{

MessageBox.Show(“cold”);

}

By: S. Sabraz Nawaz

Example


Checking More Conditions Using if Statements

• You can also create a decision structure that evaluates multiple conditions

to make the final decision using the if-else-if statement

• In C#, the generic format is:if (expression)

{

}

else if (expression)

{

}

else if (expression)

{

}

…

else

{

}


Checking More Conditions Using if Statements


Improved Marks Processor


Logical Operators

• The logical AND operator (&&) and the logical OR operator (||) allow you

to connect multiple Boolean expressions to create a compound expression

• The logical NOT operator (!) reverses the truth of a Boolean expression

Operator Meaning Description

&& AND Both subexpression must be true for the compound expression to be true

|| OR One or both subexpression must be true for the compound expression to be true

! NOT It negates (reverses) the value to its opposite one.

Expression Meaning

x >y && a < b Is x greater than y AND is a less than b?

x == y || x == z Is x equal to y OR is x equal to z?

! (x > y) Is the expression x > y NOT true?

By: S. Sabraz Nawaz

Sample Decision Structures with Logical Operators

• The && operatorif (temperature < 20 && minutes > 12)

{

MessageBox.Show(“The temperature is in the danger zone.”);

}

• The || operatorif (temperature < 20 || temperature > 100)

{

MessageBox.Show(“The temperature is in the danger zone.”);

}

• The ! Operatorif (!(temperature > 100))

{

MessageBox.Show(“The is below the maximum temperature.”);

}

By: S. Sabraz Nawaz

Nested Decision Structures

• You can create nested decision structures to test more than one condition.

• Nested means “one inside another”

• In C#, a generic format is:

if (expression)

{

if (expression)

{

statements;

}

else

{

statements;

}

}

else

{

statements

}

By: S. Sabraz Nawaz

A Sample Nested Decision Structure


Salary >= 40000

yearsOnJob>= 2

Display “Minimum salary requirement

not met.”

Display “You qualify for the load.”

Display “Minimum years at current job

not met.”

End


if (salary >= 40000)

{

if (yearOnJob >= 2)

{

decisionLabel.Text = "You qualify for the loan."

}

else

{

decisionLabel.Text = "Minimum years at current " + "job not met."

}

}

else

{

decisionLabel.Text = "Minimum salary requirement " + "not met."

}

By: S. Sabraz Nawaz


if (strCustomerType == "R")

{

if (dblSubtotal >= 100)

decDiscountPercent = .2m;

else


}

else // customerType isn't "R"



Example

• This program checks if

the mark’s range is

above 100 or below 0

(zero).

• If the mark is out of

range (0-100), an error

message is show using

the MessageBox.

• If it is within the range,

calculation is executed.


Example

By: S. Sabraz Nawaz Slide

24

switch

The switch Multiple-Selection Statement

• C# provides the switch multiple-selection statement to perform

different actions based on the possible values of an expression.

• Each action is associated with the value of a constant integral

expression or a constant string expression that the variable or

expression on which the switch is based may assume.

• A constant integral expression is any expression involving

character and integer constants that evaluates to an integer

value or a constant.

• A constant string expression is any expression composed of

string literals that always results in the same string.

• A switch statement compares ONE variable against

MULTIPLE possible values


26


27

The syntax of the switch statement

Supported data types: bool,

char, String, integral, or enum

Sample switch Statement

switch (month)

{

case 1:

MessageBox.Show(“January”);

break;

case 2:

MessageBox.Show(“February”);

break;

case 3:

MessageBox.Show(“March”);

break;

default:

MessageBox.Show(“Error: Invalid month”);

break;

}

month

Display “January”

Display “February”

Display “March”

Display “Error: Invalid month”


switch Example I: Lottory


30

switch Example II: Month Finder

switch (strCustomerType)

{

case "R":

case "C":


break;

case "T":


break;

}


31

A switch statement that falls through the first case label

GUI Design


32

GUI – CheckBox• A small area on a computer screen which, when selected by the user,

shows that a particular feature has been enabled. A CheckBox control

allows users to select a single or multiple options from a list of options.

• A typical CheckBox control has two possible states:

o Checked state is when the CheckBox has check mark on

o Unchecked is when the CheckBox is not checked

• Typically, we use a mouse to check or uncheck a CheckBox

• Checked property is true when a CheckBox is in checked state


GUI – CheckBox…


CheckedChanged Event

• Like the Click event for a button, the checkbox has

CheckedChanged as its default event.

• The CheckedChanged event occurs when the value of the

Checked property changes


GUI – RadioButton• A RadioButton control provides a round

interface to select one option from a number of options.

• Radio buttons are usually placed in a group on a container control such as a Panel or a GroupBox and one of them is selected.

• A typical RadioButton control has two possible states:

o Checked state is when the button has check mark on

o Unchecked is when the button is not checked

• Typically, we use a mouse to check or uncheck

• Checked property is true when a radiobutton is in checked state

• At a time only one radiobutton can be selected within a container


GUI – RadioButton…


GUI - PictureBox

• You can display images on your form by using the PictureBox

control.

• It is a simple control which has a main purpose of displaying

images.

• All you have to do is browse for the desired image and Visual

Studio will import it to your project. You can use several

image formats such as JPEG, GIF, PNG, and BMP.


Properties Description

Image The image that will be displayed by the control.

ImageLocation The path of the image to be displayed by the PictureBox.

SizeMode Tells how the image will be displayed.

GUI – PictureBox…• To display an image using the PictureBox control, there are multiple ways

you can use. You can go to the Properties Window and find the Image

property. Click the button to the right of it to bring out the Select Resource

Dialog.


GUI – PictureBox…

• Once the image is displayed, it may not look like you want it

to. If the loaded image is larger the size of the PictureBox,

then the image will be clipped.

• You can use the SizeMode property to change the way the

image is positioned or resized inside the control.


PictureBoxSizeMode Description

NormalThe image will be positioned in the upper-left corner of the PictureBox and if the image

is larger than the PictureBox, the image will be clipped.

StretchImage Resizes the image to match the size of the PictureBox.

AutoSize Resizes the PictureBox to match the size of the image.

CenterImageThe image is centered inside the PictureBox. If the image is larger than the PictureBox,

the image will be clipped.

Zoom Fits the whole image inside the PictureBox while maintaining the image’s size ratio.

THANK YOU


no slide title - sabraz...2017/07/04 · the if / else statement• an if-else statement will...

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