An Introduction to Control Structures

1
An Introduction to Control Structures

• Tutorial 1

2
Objectives

• Explain the sequence, selection, and repetition
  structures
• Write simple algorithms using the sequence,
  selection, and repetition structures

3
Concept Lesson
4
Defining Control Structures

• All computer programs, no matter how simple or
  how complex, are written using one or more of
  three basic structures
• Sequence
• Selection
• Repetition

5
The Sequence Structure

• Directs the computer to process the program
  instructions, one after another, in the order
  listed in the program
• Rob, the mechanical man
• Has limited instruction set (walk, turn, and sit)

6
The Sequence Structure
7
The Repetition Structure

• Makes a decision, then takes appropriate action
  based on that decision
• Example shampoo bottles typically include the
  repetition structure in the directions for
  washing your hair

8
The Repetition Structure
9
The Repetition Structure
10
Robs New Instruction Set
11
The Selection Structure

• Directs the computer to repeat one or more
  instructions until some condition is met, at
  which time the computer should stop repeating the
  instructions
• Example Selection structure is used every time
  you drive your car and approach an intersection

12
The Selection Structure
13
Application Lesson
14
Programming Rob the Mechanical Man

• To install the Rob the Mechanical Man files on
  your computers hard disk
• Click the Start button on the taskbar, and then
  click Run to open the Run dialog box
• Click the Browse button to open the Browse dialog
  box. Open the Rob Installation Files folder,
  which is located in the CppNet folder on your
  computers hard disk

15
Programming Rob the Mechanical Man

• Click Setup (Setup.exe) in the list of filenames,
  and then click the Open button to return to the
  Run dialog box
• Click the OK button in the Run dialog box. A
  message box appears and indicates that seven
  files are being copied to your computers hard
  disk
• Read the message in the dialog box. If necessary,
  close any open files, then click the OK button in
  the dialog box

16
Installation Message
17
Programming Rob the Mechanical Man(Cont.)

• As the dialog box indicates, the files will be
  installed in the Program Files\Rob directory
  (folder) on your computers hard disk. You can
  use the Change Directory button to install the
  files in another directory
• If desired, change the default installation
  directory to one of your choosing

18
Programming Rob the Mechanical Man(Cont.)

• Click the Click here to begin setup button in the
  dialog box. The Rob the Mechanical Man Choose
  Program Group dialog box opens and shows Rob the
  Mechanical Man selected in the list of groups
• Click the Continue button. When the message Rob
  the Mechanical Man Setup was completed
  successfully appears, click the OK button

19
Rob and the Flower Bed
20
Running the Application

• To run the application that you will use to
  create Robs algorithm
• Click the Start button on the taskbar, and then
  point to All Programs on the Start menu
• Point to Rob the Mechanical Man on the All
  Programs menu, and then click Application Lesson.
  The Rob the Mechanical Man application shown in
  Figure 1-13 appears on your screen

21
Rob the Mechanical Man Application
22
Initial Algorithm for Rob
23
Initial Algorithm for Rob (Cont.)
24
Final Algorithm for Rob
25
Entering the Algorithm

• To enter the algorithm shown in Figure 1-15, and
  then verify that it works correctly
• Scroll down the Instruction Set list box until
  you see the repeat 6 times instruction.
  Double-click repeat 6 times in the Instruction
  Set list box
• Double-click if the flower is red, then do this
  (inside loop) to copy this instruction to the
  Algorithm list box
• Double-click pick up the flower with your right
  hand (inside loopselection) to copy this
  instruction to the Algorithm list box
• Double-click otherwise, do this (inside loop),
  then double-click pick up the flower with your
  left hand (inside loopselection)

26
Entering the Algorithm (Cont.)

• Scroll down the Instruction Set list box, if
  necessary, until you locate the walk (inside
  loopselection) instruction, then double-click
  walk (inside loopselection)
• Double-click walk (outside loopselection)
• Click the Verify Algorithm button. The Verify
  message box opens and displays the Great job!
  message. Click the OK button to close the message
  box
• Click the Exit button to close the application

27
First Instruction
28
Completed Algorithm
29
Uninstalling Rob the Mechanical Man

• Click the Start button, and then click Control
  Panel on the Start menu
• Click Add or Remove Programs to open the Add or
  Remove Programs window
• Scroll down the list of currently installed
  programs, if necessary, then click Rob the
  Mechanical Man in the list. Click the
  Change/Remove button. When you are asked if you
  are sure you want to remove Rob the Mechanical
  Man and all of its components, click the Yes
  button
• When the Program installation removed message
  appears, click the OK button
• Click the Close button to close the Add or Remove
  Programs window, then close the Control Panel
  window

30
Summary

• Basic components of all algorithmic problem
  solutions
• Sequence
• Process instructions one after another
• Selection
• Take an action based on a decision
• Repetition
• Repeat a set of instructions until a condition is
  met
• Write simple algorithms using the sequence,
  selection, and repetition structures