Decision Structures

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Decision Structures

• How to make your algorithm follow more than just
  one path

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If
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IF Flowchart
Decision
T
F
Do if true
Do no matter what
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IF Pseudocode

• If TextBox shows the right answer then
• Output Correct!
• Disable button
• End if

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If Problem

• You have a program where people enter info about
  themselves, including their birthday in the
  format mm/dd.
• Its rare to be born on 02/29, so output a
  message to all those people saying, Congrats!
  You were born on Leap Day!
• After that the program should continue as normal
  and ask for their occupation.

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Flowchart
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Pseudocode

• If

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If-Else
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If-Else
Decision
T
F
Do ELSE steps
Do IF steps
Continue in either case
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IF-ELSE Pseudocode

• If TextBox shows the right answer then
• Output Correct!
• Disable button
• Else
• Output Sorry, try again!
• End if

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If-Else Problem

• You want to get an average score for the class
  (AverageScore), so you need to divide TotalScores
  by NumberStudents, but you cant divide by zero
  or the program will crash.
• Check if the user has entered zero if so, dont
  do the calculation and output a message stating
  the error.
• If there is no zero problem, do the calculation
  and output the answer.
• After either process, increment Counter by one

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Flowchart
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Pseudocode

• If

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While Loop
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While Loop
Change looping variable
Decision
T
Stuff you want to repeat
F
Continues after decision is false
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WHILE Pseudocode

• Counter 1
• While counter is less than 4
• If TextBox.Text is correct then
• Output Correct!
• Disable button
• Else
• Output Sorry, try again.
• End if
• End while
• Output Sorry, youve used up your guesses.
• Disable button

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While Problem

• You want to add all the numbers between zero and
  the positive number the user enters (Number)
• After the loop is finished, output Sum

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Flowchart
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Pseudocode

• While

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Repeat (loop of uncertain length)
T
Decision
Repeats until decision is false
F

• Decision made at END of loop

Continues after decision is false
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Example REPEAT Structure

• Repeat
• Output Sorry, try again!
• Until TextBox shows right answer
• Output Correct!
• (continually tests the TextBox needs no enter
  button code attached to TextBox)

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For-To (loop of certain length)
Change counter by one
Decision defines counter
This gets repeated
T
F
Continues after counter finished
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Example FOR-TO Structure

• COUNTER 1
• For COUNTER 1 to 5
• Allow input (TextBox)
• Allow test (attached to Button)
• If-Else decision structure
• Add one to COUNTER
• End for
• Output Sorry, you used up your 5 guesses
• Disable button
• (attached to main form each time the button is
  pressed, the counter goes up)