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					Software Development
Programming Language Features – Loops


                                        1
Lesson Aims and Objectives

After completing this topic, you should be able to:


1. Use a list box for scrolling output
2. implement fixed loops using For..Next

3. use a counter in a fixed loop

4. implement conditional loops using Do .. Loop Until

5. Use Random numbers

6. Compare Do .. Until and Do .. While loops


                                                        2
Repetition using For ..Next


 Design, write and test a program to display the
 message “Hello” 25 times

 Fixed Loop
 With a fixed loop the programmer knows in
 advance how many times the instructions within
 the loop are going to be executed

 Look at the design of the solution on page 3 of
 Topic 4 notes.


                                                   3
Configuring The Number Of Times The
Fixed Loop Runs

 Can we change the program so that we can repeat
 the instructions within the loop by a number that
 is entered by the user?

 1. Enter, test and print the code on page 4 of
 Topic 4 notes




                                                  4
Counting using a Fixed Loop

 Can we use a fixed loop to display a count?

 1. Design, write and test a program to display the
 message 1,2,3,4,5, … 99,100

 2. Look at the design of the solution on page 6 of
 Topic 4 notes.

 3. Do the implementation task on page 7 of the
 notes
 4. Try modification (1) and modification (6) on
 page 7

  ***** Do Assessment 4: For Loops *****
                                                5
Lesson Aims and Objectives

After completing this lesson, you should be able to:

1. implement conditional loops using Do .. Loop Until

2. Use Random numbers

3. Compare Do .. Until and Do .. While loops




                                                        6
Do .. Loop Until

What about times when the number of repetitions is not
known in advance?

For example, a quiz program might give the user repeated
chances to get the answer correct. The programmer doesn’t
know in advance whether the user will get the question right
first time, or take 2, 3, 4 or more attempts.


         Do
                 Line(s) of code
                 to be repeated

         Loop Until condition
                                                         7
Example – Do .. Loop Until


                          Page 8 of Topic 4




  1.   Enter code
  2. Test, screenshot and print




                                              8
Random Numbers

Visual BASIC provides the programmer with a pre-defined
function Rnd to generate random numbers.

The Rnd function produces random numbers between 0 and
1.
To produce random whole numbers between 1 and 10, we
need to do 3 things:
        1. multiply by 10 to produce a random
        fraction between 0 and 10
       2. “chop off” the fraction part using the pre-
       defined function Int
       3. add 1, otherwise the highest number will
       always be 9, as it is rounded down by the Int
       function.
                                                        9
Example - Random Numbers

   Private Sub cmdStart_Click()
     ' generates list of random number

     Dim number As Integer
     Dim counter As Integer
     lstRandoms.Clear

     For counter = 1 To 10
       number = Int(Rnd * 10) + 1
       lstRandoms.Additem(number)
     Next counter

   End Sub
                                    10
Truly Randomised

If this program runs then it will always generate THE
SAME SET of random numbers.

 Private Sub cmdStart_Click()
   ' generates list of random number

   Dim number As Integer
   Dim counter As Integer

   Randomize
   lstRandoms.Clear

   For counter = 1 To 10
     number = Int(Rnd * 10) + 1
     lstRandoms.Additem(number)
   Next

 End Sub
                                                        11
Practical Do .. Loop Until with random


                          Code at foot of Page 12




  1.   Enter code
  2. Test, screenshot and print




                                                    12
Finishing Off

1. Look at example 3.6.1. on page 14 (CLASS LISTS)

2. Carefully study the pseudocode and how you
represent looping – you will need to know how to do this
for the next assessment task

3. Complete Stage 3 (implementation) and stage 4
(Testing) on Page 15

4. Study 4.7 Other Forms of Conditional Loop on page 17

5. Read the Summary of Topic 4 on page 18




                                                           13

				
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posted:8/28/2012
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