Conditional statements
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If statements allow a program to control the flow of execution based on whether a condition is true or false. An If statement contains a condition and one or more branches of code. If the condition is true, the first branch executes; if false, the second branch executes. ElseIf allows multiple conditions to be checked. Nesting If statements means placing an entire If statement inside the True or False branch of another. Select Case provides an alternative to nested If/ElseIf for choosing between multiple options.
Conditional statements
- 2. If Statement • VBA uses 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 Condition true? 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 If varA > 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 If Statement 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
- 8. Single Branch If Statement Flowchart Condition true? yes no Perform action Bringing the branches back together gives the flowchart a better structure 8
- 9. Multiple Branch If Statement 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 If Statement 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 inside of 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
- 12. 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
- 13. 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
- 14. 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
- 15. Case Statement Example Assume position 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 looked at 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