27/05/ Iteration Loops Nested Loops & The Step Parameter

227/05/2016 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.

327/05/2016 For … To … Next e.g. Display the numbers from 1, 3, 5, 7, 9 Dim Number As Integer Dim Number As Integer For Number = 1 To 10 Step 2 For Number = 1 To 10 Step 2 lblNumber.Text = Number Next Number Next NumberNote: This loop will not display 11 as it is bigger than the 10 allowed This loop will not display 11 as it is bigger than the 10 allowed

427/05/2016 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 minute hand would be the outer loop. The second hand would be the inner loop. The second hand would be the inner loop.

527/05/2016 General Form of a nested For … To … Next Iteration Loop For (variable identifier = start value) To (end value) (Outer loop body statements) … (Outer loop body statements) … For (variable identifier = start value) To (end value) For (variable identifier = start value) To (end value) (Inner loop body statements) … Next (variable identifier) Next (variable identifier) (Outer loop body statements) … (Outer loop body statements) … Next (variable identifier) InnerLoop OuterLoop

627/05/2016 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) Console.WriteLine(“OuterNumber variable is ” & OuterNumber) For InnerNumber = 1 To 2 For InnerNumber = 1 To 2 Console.WriteLine(“InnerNumber variable is ” & InnerNumber) Next InnerNumber Next InnerNumber Next OuterNumber

727/05/2016 A nested For … To … Next Iteration Loop The previous slide’s code will produce: OuterNumber variable is 1 OuterNumber variable is 1 InnerNumber variable is 1 InnerNumber variable is 2 OuterNumber variable is 2 OuterNumber variable is 2 InnerNumber variable is 1 InnerNumber variable is 2 OuterNumber variable is 3 OuterNumber variable is 3 InnerNumber variable is 1 InnerNumber variable is 2 OuterNumber variable is 4 OuterNumber variable is 4 InnerNumber variable is 1 InnerNumber variable is 2

827/05/2016 Constants Used when: The user does not provide the value. The user does not provide the value. You don’t want the value to change during the program. 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.

927/05/2016 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 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. It makes the code more meaningful to anybody reading it.

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)

1127/05/2016 Program 3.2a Addition Table Specification: Write a program to display the sum of row and column numbers. Write a program to display the sum of row and column numbers.

1227/05/2016 Program 3.2a Addition Table Create a new project named ‘Addition Table’.

1327/05/2016 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. 'Enter column numbers with 8 spaces in between. Console.Write(ColNumber & Space(8)) Console.Write(ColNumber & Space(8)) Next ColNumber Continued on next slide.

1427/05/2016 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. 'Enter first number in the row. Console.Write(RowNumber & Space(12)) Console.Write(RowNumber & Space(12)) For ColNumber = 0 To Max 'Start of inner loop. 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 ColNumber 'End of inner loop. Console.WriteLine() ’Start a new empty line. Console.WriteLine() ’Start a new empty line. Next RowNumber 'End of outer loop.

1527/05/2016 Program 3.2a Multiplication Table Run the program and test it.

Given pseudocode will use the following structure: FOR ← TO STEP ENDFOR

1727/05/2016 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 Courier New font (as this a fixed width font which means each character has the same width). Use Courier New font (as this a fixed width font which means each character has the same width). Use an If …Then … End If statement to add less spaces when necessary. 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.

1827/05/2016 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) … (Loop Body statements) … Next (variable identifier)

1927/05/2016 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: 3.1 For To Next Loops3.1 For To Next Loops 1.As before: to count up from a lower first number to a higher second number. 2.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. 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. New If statement, just after this, to see which option has been chosen. Leave the original main code for option 1. 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. 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 To count down write Step -1 at the end of the For … To … Step -1Extension: Show only numbers between the two values not the values themselves. 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? 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.

2027/05/2016 Plenary What is the step parameter used for? Used to increase the variable identifier in a For … To … Next loop by more than 1. Used to increase the variable identifier in a For … To … Next loop by more than 1.

2127/05/2016 Plenary What is the general form of a nested For … To … Next loop? For (variable identifier = start value) To (end value) For (variable identifier = start value) To (end value) (Outer loop body statements) … For (variable identifier = start value) To (end value) (Inner loop body statements) … (Inner loop body statements) … Next (variable identifier) (Outer loop body statements) … Next (variable identifier) Next (variable identifier) InnerLoop OuterLoop