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Software Development. Programming Language Features – Loops. 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.
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Software Development Programming Language Features – Loops
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
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.
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
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 *****
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
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
Example – Do .. Loop Until Page 8 of Topic 4 • Enter code • Test, screenshot and print
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.
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
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
Practical Do .. Loop Until with random Code at foot of Page 12 • Enter code • Test, screenshot and print
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
