If statements /conditional execution)If you have any questions about the Unit III Practice items or the sample Comp.Demo. I distributed, now is the time to ask.
We will begin consideration of the programming fundamental of selection. But we will halt at 4:10 pm to allow time for the competency demo for Unit III.
At the start of the course, I mentioned the basics of computing—data & actions and the basics ways of organizing actions—sequence, selection, repetition, and modularization. Programming is figuring out what actions are needed and then organizing them in a way that accomplishes our overall task.
This entails knowing each action and its dependencies (what it depends on and what depends on it). The things it depends on must come before the action and the action itself must come before those things that depend on it.
Selection is deciding which action to take in a given situation or perhaps to take no action at all. Again, the action may depend on something happening before it in order to take the action or to decide whether to take the action. Things that depend on the action being taken (or not) must be placed after it.
Repetition simply repeats some set of actions. Again, some actions may need to occur before the repeated actions or in order to test for the repetition and some actions may need to be sequenced after the repetition.
Modularization is merely putting some actions together and giving them a name. This allows you to "see" the action without getting bogged down in details. It also allows you to take the action from different places in your program without duplicating the code
So, what does today's topic, "selection" look like. You are familiar already with the idea of if something is true, do something. That is selection. In programming we have an If statement; actually we have several variations of the If statement. The two basic forms are:
' actions required before the IF If true Then ' set of actions End If ' actions required after the IF
and
' actions required before the IF If true Then ' set of actions Else ' alternate set of actions End If ' actions to occur after the IF
Questions? ... Let's explore the various parts and see what we can deduce about the If statement.
That is how the if statement works. Questions? Comments? Wonderings?
There is one particular way of using if statements that you should be aware of—as a flag. Sometimes there are multiple occasions to test a condition and any or all of the tests could determine the action to be taken when all tests are completed. The pattern here is something like the following.
Dim okay As Boolean = True ... If <bad test 1> Then okay = False End If If <bad test 2> Then okay = False End If . . . If okay Then ' do okay action else ' do NOT okay action End IF
Next, we will look at slightly more complex examples and alternatives for doing them. Let's look at an example involving a student asking about their grade (its a silly example, but one we are familiar with). Even a simple problem like get a score from the user and determine the grade involves some thinking in order to code it correctly. Some considerations are:
So a simple IF statement could check to see if the user entered a number for a score. Typically we want to do something with the score once we know the input is okay. That would go in the ELSE part of the IF we did above.
Here is some example code—what was done in class may differ.
Ifs
Dim valueIn As String = txtScore.Text
Dim score As Double
Dim grade as String
If IsNumeric(valueIn) Then
score = Val(valueIn)
If score >= 90 Then
grade = "A"
End If
If score < 60 Then
grade = "F"
End IF
If score >= 80 And score < 90 Then
grade = "B"
End If
If score >= 70 And score < 80 Then
grade = "C"
End If
If score >= 60 And score < 70 Then
grade = "D"
End IF
MessageBox.Show("The grade is " & grade)
Else
MessageBox.Show("Please enter a numeric score.")
End If
Ifs
Dim valueIn As String = txtScore.Text
Dim score As Double
Dim grade as String
IfIsNumeric(valueIn) Then
score = Val(valueIn)
If score >= 90 Then
grade = "A"
ElseIf score >= 80 Then
grade = "B"
ElseIf score >= 70 Then
grade = "C"
ElseIf score >= 60 Then
grade = "D"
Else
grade = "F"
End IF
MessageBox.Show("The grade is " & grade)
Else
MessageBox.Show("Please enter a numeric score.")
End If
Dim okToOrder As Boolean = True
Dim order As String = ""
If rdo8in.Checked Then
order = order & "8 inch "
ElseIf rdo12in.Checked Then
order = order & "12 inch "
ElseIf rdo16in.Checked Then
order = order & "16 inch "
ElseIf rdo20in.Checked Then
order = order & "20 inch "
Else
MessageBox.Show("Size NOT selected")
okToOrder = False
End If
' Similar code for checking to see if a crust was selected
' It would continue using the "okToOrder" variable or FLAG
' Similar code for checking to see if a type of pizza was selected
' It would continue using the "okToOrder" variable or FLAG
If okToOrder Then
lstOrder.Items.Add( order )
End If
Remember, you need to be deciding on a project. Review the project assignment description noting the project checklist information. Think about "apps" that might be useful in your field. If you can't think of anything, talk with your friends or come see me. We have the next three weeks or so to do meetings about your project, and, I will be gone March 8 - 12.
Questions? Comments? Wonderings?
If students are ready, complete the Unit IV competency demo.
Remember that the project proposal meeting needs to occur soon. Listed due date is this Friday but I'll change that to next Tuesday. Questions about the project?
If students are ready, complete the Unit IV competency demo.