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B065: PROGRAMMING. OPERATORS AND SELECTION 1. Starter. Have a go at the All Logic Signs activity. COMP1 Programming 8 Selection All Logic Signs.xls. Objectives. Understand what is meant by selection in programming. Explore selection programming commands: IF - PowerPoint PPT Presentation
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B065: PROGRAMMINGOPERATORS AND SELECTION 1
Starter Have a go at the All Logic Signs activity.
COMP1 Programming 8 Selection All Logic Signs.xls
Objectives• Understand what is meant by selection in programming.
• Explore selection programming commands: IF
• Understand the use of logical operators.
Operators Recap• Answer these questions with a TRUE or FALSE
• 6 > 3• 72 < 75• 115 >= 115• 92 > 42+2• 12 = 6+6• 32 <= 16*2
> MORE than
< LESS than
<= LESS than or EQUAL to
>= MORE than or EQUL to
Logical Operators in Programming
Evaluation Symbol Example
Equal to = Number = 1
Less Than < Age < 21
Less Than or Equal To <= Age <=17
Greater Than > Debt > 25
Greater Than or Equal To >= Debt > = 2000
Not Equal To <> Number <> 1
AND AND Number = 1 AND Age < 12
OR OR Number = 1 OR Number = 2
NOT NOT NOT Age < 17
IF Logic Recap
Which goes where to make a logical sentence? Let’s do one at a time. CLICK on a question mark to reveal.
What you believe in…
Question What to do if TRUE What to do if FALSE
IF 12 > 25 Clap twice Clap once
IF you are at Crypt Stand up, then sit down Spin your head around
IF 30 < 42 Wink twice Shake your hands
IF 12 > 6*1 Put your hands up Click twice
IF you are in ICT Stand up, turn around, sit back down
Yawn
IF 4*2 >= 12 Roar like a lion Moo like a cow
You will be given a logical question. If you think it is TRUE, do what is says under TRUE. If you think it is FALSE, do the FALSE action.
A Separate Example• Let’s look at a spreadsheet version (From GCSE) which you
should be familiar with.
• It nicely sets the scene for selection in programming.
• IF Example
IF…THEN…END IF• Sometimes in programming, you may only want to execute
lines of code if certain conditions are met.
• For example, you would not send out a bill to a customer if they did not owe anything.
• The way to write an IF statement is simple:
If <condition> Then <statements>End If
ExamplesIf score = 100 Then Console.WriteLine("Full Marks!")End If
If pay > tax Then pay = pay - taxEnd If If mark < 40 Then result = "Fail" console.writeline(result)End If
The semantics are simple: if the condition is True, the following statement(s) will be executed; otherwise they will be omitted.
If, Then, and End If are all keywords - the code editor will capitalise them and colour them blue when you finish typing any of them, as it does with all keywords.
What can you use?• The statements can be any legal VB statements - and that includes If … Then … End
If statements now! So we can quite easily have a nested structure, like the following example:
If age > 65 Then If theDay = "Thursday" Then 'Senior Citizens get a 10% discount! cost = 0.9 * cost End IfEnd If
• Note that each If requires a corresponding End If. See how we INDENT to make the code easier to understand.
IF…THEN…ELSE…END IF• What if you want some code to be executed if the condition IS
NOT met?
If mark < 40 Then result = "Fail" Else result = "Pass"End IfConsole.WriteLine(result)
• You can use ELSE. What happens in the code above?
Multiple Conditions? ELSEIF• What if you have multiple conditions (or rules) which you
want to check?
Summary• IF…END IF Basic Checks.
• IF…ELSE…END IF Basic Checks with a catch situation.
• IF…ELSEIF…ELSE…END IF Multiple conditions.
• You can also use logical operators ( >, >=, <, <=, AND, OR, NOT) in your selection statements.
TASK• Complete the questions in your guide.
• Attempt Tasks 10, 11 and 12.
• We will go through each task throughout the lesson.
• Complete for homework.
Objectives Review• Understand what is meant by selection in programming.
• Explore selection programming commands: IF
• Understand the use of logical operators.
Required Reading• Each week you will be given required reading.
• If you fail to do this, you will 100% find the lessons which follow it EXTREMELY difficult.
• Before next lesson you should have read:
• Read Chapter 4• Homework – Finish exercises 1-10 Chapter 4
Plenary• If the day is Monday and a person is 18 or over (but younger
than 21), they qualify for a discount on drinks over £2. They receive 35p off the price of the drink.
• What would be the IF block which would express this in code?