Arrays and others

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Arrays and others
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Annoucement

• Todays office hour move to Friday 100PM to
  300PM
• Today
• Call by reference and call by value
• Variable scopes
• Arrays
• Debugging

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Call by reference

• Passing the whole variable memory block to the
  sub procedure
• If inside is changed, outside will be changed
  too.
• How
• Private Sub Add(num1 as integer, num2 as integer)
• Call Add(x,y)

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Call by value

• Only copy the value of the variable to the sub
  procedure.
• Inside changes will not affect the outside
  variables.
• How
• Private Sub Add(num1 as integer, num2 as integer)
• Call Add((x),y)
• Call by reference and call by value also apply to
  the function procedure.
• When to use.

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Scope of a variable

• Local scope.
• Variable declared in a sub procedure
• It only exists in this sub procedure.
• Form-level scope.
• Variable declared out of any sub procedure.
• Any sub procedure can read it.

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Arrays

• Array is a special type of variable
• Regular Variables hold one value
• Arrays hold may values - subscripts
• X(1), X(2), X(3), X(4), X(5)
• Arrays are like subscripts refer to different
  values stored in the same variable
• Pp. 175-187

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What Arrays Do

• Suppose Data is an array.

Data(1) Data(2) Data(3) Data(4) Data(5)
First value Second value Third value Fourth value Fifth value
22.49 13.42 22.17 64.11 7.33
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Declaring Arrays

• Use Dim key word to declare arrays, just as what
  we do for variables.
• Dim Data(1 to 50) As Single
• Dim Species(1 to 4) As String
• Accessing values in an array with subscript.
• Data(44) 22.5
• Species(1) ACTGACTCGTAACGT
• Red Number is INDEX

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Matrices 2-dimensional Arrays

• Declaration
• Dim Data(1 to 50, 1 to 20) As Single
• Accessing
• Data(2,4)100
• The range of the subscript can be between any
  integers.
• Dim WeekendMorning(6 to 7, 7 to 12) As String

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Passing array to a sub procedure

• Array can be passed as an argument to sub
  procedures of function procedures.
• Private Sub ProcName(ArrayName() as Integer)
• Call ProcName(Array1)
• Array can only be called by reference.
• Function Ubound(ArrayName,2)

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ReDim

• Use ReDim when declaring an array size based on a
  variable
• Also called dynamic array
• User tells you there are 50 values (count 50)
• ReDim Values(1 to count) as Single

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Decimal to Binary calculator
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Flow chart
Start
If number Equal to 1 or 0
Print The Remainder to the left of previous
remains
No
Divide the Number By 2
Get a number
Yes
Is the quotient Equal to 1?
No
Output number
Print 1 To the left of Previous remainders
Yes
End
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Convert the first decision to code

• IF number ltgt 0 OR number ltgt 1 THEN
• Do the conversion part
• END IF
• Call OutputNumber(number)

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Code fragment for the loop

• Do While quotient ltgt 1
• quotient number \ 2
• reminder number mod 2
• number quotient
• call PrintReminder()
• Loop

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Problems
Print 1 To the left of Previous remainders

• So far we have already solved the Decision
  structure and loop structure.
• Problems not solved.
• All previous reminders need to be stored.
• How many?

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Steps

• First we need determine how many places in the
  converted binary number
• Int(Log(Dec) / Log(2)) 1
• Second, declare a dynamic array to store all the
  output numbers.
• ReDim Bin(1 to binplaces) as String
• In the do while loop, put reminders of each step
  in the Bin array. Beware of the order

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Output function
Output number

• Private Sub Output(rems() As String)
• Print the binary array in the picOutput picture
  box
• End Sub

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Debugging tools in VB

• Break points

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Debugging tools in VB(2)

• Immediate Window

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Debugging tools in VB(3)

• Watch window and local window

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Friday

• Do the program that convert 10 base value to
  binary.