1. Nested Loops & The Step Parameter
3.2 Iteration Loops
Nested Loops
&
The Step Parameter
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2. Learning Objectives State what the step parameter is used for.
State the general form of a nested For … To … Next iteration loop.
How to output to the same line rather than always to a new line.
How to start an empty new line.
State how to enter spaces.
Explain what constants are and their advantages.
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3. For … To … Next e.g. Display the numbers from 1, 3, 5, 7, 9 Note:
Dim Number As Integer
For Number = 1 To 10 Step 2
lblNumber.Text = Number
Next Number
Note:
This loop will not display 11 as it is bigger than the 10 allowed
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4. A nested For … To … Next Iteration Loop
When you have one loop inside another.
Think of the outer loop as a large cog driving a smaller cog which is the inner loop.
Every time the larger cog revolves once (one repetition of the outer loop), the inner cog usually revolves more than once.
As a solid real life example think of the second and minute hand.
The minute hand would be the outer loop.
The second hand would be the inner loop.
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5. General Form of a nested For … To … Next Iteration Loop
For (variable identifier = start value) To (end value)
(Outer loop body statements) …
(Inner loop body statements) …
Next (variable identifier) O u t e r L o p I n e r L o p
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6. A nested For … To … Next Iteration Loop
Dim OuterNumber As Integer
Dim InnerNumber As Integer
For OuterNumber = 1 To 4
Console.WriteLine(“OuterNumber variable is ” & OuterNumber)
For InnerNumber = 1 To 2
Console.WriteLine(“InnerNumber variable is ” & InnerNumber)
Next InnerNumber
Next OuterNumber
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7. A nested For … To … Next Iteration Loop
The previous slide’s code will produce:
OuterNumber variable is 1
InnerNumber variable is 1
InnerNumber variable is 2
OuterNumber variable is 2
OuterNumber variable is 3
OuterNumber variable is 4
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8. Constants Used when: e.g. Const TaxRate = 0.25
The user does not provide the value.
You don’t want the value to change during the program.
e.g. Const TaxRate = 0.25
If you try to assign another value to a constant later in the program an error will occur.
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9. Constants
Using a constant rather than a number presents two advantages:
It allows the value to be changed by the programmer easily i.e. otherwise the programmer would have to go through and change the value every time it occurs.
It makes the code more meaningful to anybody reading it.
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10. To output to the same line / Create a new empty line / Display Multiple Spaces:
Console.Write(“….”)
Will output onto the same previous line so basically continues a line of outputs.
If no previous line then it will output onto a line but without creating a new one.
Console.WriteLine()
Will start a new empty line.
To enter spaces:
Space(number)

11. Program 3.2a Addition Table
Specification:
Write a program to display the sum of row and column numbers.
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12. Program 3.2a Addition Table
Create a new project named ‘Addition Table’.
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13. Program 3.2a Addition Table
Const Max = 5
Dim ColNumber As Integer
Dim RowNumber As Integer
Dim Sum As Integer
'Display '+' and '12' spaces in top right corner to start table.
Console.Write("+" & Space(12) )
For ColNumber = 0 To Max 'Simple For ... To ... Next loop
'Enter column numbers with 8 spaces in between.
Console.Write(ColNumber & Space(8))
Next ColNumber
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Continued on next slide.

14. Program 3.2a Addition Table
Console.WriteLine() ’Start a new empty line.
For RowNumber = 0 To Max 'Start outer loop.
'Enter first number in the row.
Console.Write(RowNumber & Space(12))
For ColNumber = 0 To Max 'Start of inner loop.
Sum = ColNumber + RowNumber
'Enter addition
Console.Write(Sum & Space(8))
Next ColNumber 'End of inner loop.
Next RowNumber 'End of outer loop.
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15. Program 3.2a Multiplication Table
Run the program and test it.
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16. Given pseudocode will use the following structure:
FOR <identifier> ← <value1> TO <value2> STEP <value3>
<statement(s)>
ENDFOR

17. Extension “Multiplication” Program 3.2b
Write a program to produce the following multiplication table.
Note you will have a problem with columns due to numbers >99.
Use an If …Then … End If statement to add less spaces when necessary.
Please note that I actually don’t expect you to fully solve this.
If you can then great otherwise spend around 15 minutes and then just send me what you have.
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18. The Step Parameter
Used to change the variable identifier in a For … To … Next iteration loop by something other than +1.
For (variable identifier = start value) To (end value) Step (increment value)
(Loop Body statements) …
Next (variable identifier)
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19. Extension “Between Two Numbers” Program 3.2c
Extend the “Between Two Numbers” Program from 3.1 For To Next Loops so that it has a 2 options:
As before: to count up from a lower first number to a higher second number.
Count down from a higher first number to a lower second number.
Hints:
Ask the user for option 1 or 2, before the main code.
New If statement, just after this, to see which option has been chosen.
Leave the original main code for option 1.
Copy and paste the original main code into the ElseIf for option 2 and adjust as necessary.
To count down write Step -1 at the end of the For … To … Step -1
Extension:
Show only numbers between the two values not the values themselves.
What happens if the second number is higher than the first number when this new second button is clicked?
The loop does not end and results in what is called an infinite loop, resulting in VB skipping the loop.
The new “second” option should not allow the second number to be higher than the first number.
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20. Plenary What is the step parameter used for?
Used to increase the variable identifier in a For … To … Next loop by more than 1.
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21. Plenary What is the general form of a nested For … To … Next loop?
For (variable identifier = start value) To (end value)
(Outer loop body statements) …
(Inner loop body statements) …
Next (variable identifier) O u t e r L o p I n e r L o p
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