Conditional statements

Conditional statements

• 1.
  Conditional Statements 1
• 2.
  If Statement • VBAuses Boolean expressions, along with If statements, to control the flow of execution of a program If condition Then ‘here condition is a Boolean expression action1 Else action2 End If 2
• 3.
  If Statement Flowchart Conditiontrue? yes no Perform action 1 Perform action 2 Bringing the branches back together gives the flowchart a better structure 3 The arrows are one-way streets. Only one action can (and must) be performed.
• 4.
  If Statement Example IfvarA > varB Then max = varA min = varB Else max = varB min = varA End If • Note: In real life we would use the Max and Min functions but we are keeping things simple to start with 4
• 5.
  If Statement Example ‘compute shipping charge, with a discount for more expensive orders If price >= discountShippingPrice Then shippingCharge = price * discountShippingChargeRate Else shippingCharge = price * regularShippingChargeRate End If totalCharge = price + shippingCharge 5
• 6.
  If Statement Options •The Else part can be omitted: If condition Then action1 End If • There can be multiple ElseIf branches If condition1 Then ‘if condition1 is True do action1, end action1 ElseIf condition2 Then ‘if condition1 is F & condtion2 is T, do action2 action2 Else ‘if both conditions are F, do action3 action3 EndIf 6
• 7.
  Single Branch IfStatement Example ‘ compute shipping charge if applicable shippingCharge = 0 If price < freeShippingPrice Then shippingCharge = price * shippingChargeRate End If price = price + shippingCharge ‘ if the If statement interior is not executed, then shippingCharge is 0 7
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  Single Branch IfStatement Flowchart Condition true? yes no Perform action Bringing the branches back together gives the flowchart a better structure 8
• 9.
  Multiple Branch IfStatement Example ‘ Set thank you message based on tip size tipPercent = (tipAmount/baseCharge) * 100 If tipPercent < 15 Then txtThankYou.Text = “Thanks.” ElseIf tipPercent < 20 Then txtThankYou.Text = “Thank you and have a nice day.” ElseIf tipPercent < 25 Then txtThankYou.Text = “Thank you very much! Have a nice day.” Else ‘we know the tip is at least 25% txtThankYou.Text = “Thank you!! Have a GREAT Day!” End If 9
• 10.
  Multiple Branch IfStatement Flowchart Condition 1 true? yes no Perform action 1 10 no no yes yes Perform action 2 Perform action 3 Perform else action Condition 2 true? Condition 3 true? The else is optional. The arrows are one- way streets
• 11.
  Nesting: If’s insideof If’s • You can nest entire If statements inside the If or Else part of another If statement • Nesting more than one or two deep is strongly discouraged! It makes the program hard to read and understand • Try to use Elseif or more complex conditions instead 11
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  Nested If’s Example ‘Select title based on language and gender If language = “French” Then If gender = “Female” Then title = “Mademoiselle” Else title = “Monsieur” Endif ElseIf language = “English” Then If gender = “Female” Then title = “Miss” Else title = “Mister” EndIf Else title = “” ‘no title in this case EndIf 12
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  Converting to ElseIfs ‘Select title based on language and gender If language = “French” And gender = “Female” Then title = “Mademoiselle” ElseIf language = “French” And gender = “Male” Then title = “Monsieur” ElseIf language = “English” And gender = “Female” Then title = “Miss” ElseIf language = “English” And gender = “Male” Then title = “Mister” Else title = “” ‘ it’s usually best to have an else case EndIf 13
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  Select Case Statements •The Select Case Statement can be used when there are multiple options to choose from • It can simplify program structure • It makes the logical structure of the program clear when a nested if or long Else If structure might not 14
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  Case Statement Example Assumeposition is a variable with a value between 1 and some number from 2 to 50 Select Case postion Case 1 txtOutcome.Text = “Win” ‘several lines could go here Case 2 txtOutcome.Text = “Place” Case 3 txtOutcome.Text = “Show” Case 4,5 txtOutcome.Text = “Close but no cigar” Case Else txtOutcome.Text = “Out of the money” End Select 15
• 16.
  Conditionals Overview We’ve lookedat program elements that let us write conditions and branches in programs: – Boolean constants True and False – Comparison operators to form Boolean expressions – Boolean operators to build more complex expressions; truth tables to check them – If statements, three types (with Else, with no Else, with ElseIfs) – Nested If’s – Select Case statements