MA3696 Lecture 5

LECTURE 5

More loops
1D Arrays

SUMMARY
Looping userform controls
Generalising loops
Nested For-Next loops
1D Arrays

MORE FOR-NEXT LOOPS

Loop Controls

LOOPING USERFORM CONTROLS
Labels 1,
2 and 3

Public Sub Command_LoopControls_Click()

Label1.Caption = Cells(2, 2).Value
End Sub
These values are changing

Public Sub Command_LoopControls_Click()
i=1

i=2
i=3


End Sub
The label is i

The column
is i + 1


The (Name) of the
userform control


Use concatenation


Use the ith label


The column
is i + 1

EXERCISE 1. WRITE A FOR LOOP
Download Lecture 5 Student Example.xlsm
Write a For-Loop for this code in UserForm1.
 Remember to declare your counter!
Public Sub LoopExercise1_Click()

Range(“Investment”).Columns(1).Value = TextBox1.Value
End Sub

Questions:
 Are the cells being assigned the value of the textboxes?
 Or are the textboxes being assigned the values of the cells?

NESTED FOR-NEXT LOOP
Repeat this twice

For i = 1 to 3
Cells(i, 1).Value = i
Next i

?

Repeat this twice

For k = 1 to 2

For i = 1 to 3
Next i

Next k

Repeat this twice

For i = 1 to 3
Next i

For k = 1 to 2
For i = 1 to 3
Next i
Next k

Repeat this twice

For i = 1 to 3
Next i

For k = 1 to 2
For i = 1 to 3
Cells(i, k).Value = i
Next i
Next k

EXERCISE 2. NESTED FOR-NEXT LOOP
Use Lecture 5 Student Example.xlsm
 LoopExercise2 in Module1

Write a nested For-Loop for this output.
 Remember to declare your counter.

Repeat this twice

EXERCISE 2. SOLUTIONS
Cells(1, 1).Value = 1

For i = 1 to 3
Cells(1, i).Value = i
Next i
Repeat this twice


For k = 1 to 2
For i = 1 to 3
Cells(1, i).Value = i
Next i
Next k


For k = 1 to 2
For i = 1 to 3
Cells(k, i).Value = i
Next i
Next k

EXERCISE 3. NESTED FOR-NEXT LOOPS
 LoopExercise3 in Module1

Write a nested For-Loop for this output.
 Remember to declare your counter.

Repeat this three times

GENERALISING CODE

Using
variables
or
constants
instead of
explicit
numbers

WHAT DOES IT MEAN TO GENERALISE?
Dim i As Integer

For i = 1 to 10
Cells(i +1, 1).Value = i
Next i
I know the number
Dim i As Integer

of TIMEPERIODS
in advance

Const TIMEPERIODS = 10
For i = 1 to TIMEPERIODS
Cells(i +1, 1).Value = i
Next i

Unknown until the user runs the program

Dim i As Integer
Dim nStocksSelected As Integer

For i = 1 to nStocksSelected
[…..]
Next i
I only want this code to run for the
number of stocks selected by the user

Replace specific numbers with variables
 And assign those variables a value

Enables code to be changed/updated quickly
 Only have to change one value instead of every value

Enables you to use user inputs in your loops
 You don’t know these in advance

ARRAYS
Hold a range (or set) of values
Basically a set of variables
Your arrays will mainly be 1 or 2 dimensions

arrayName(5)

arrayName(5)

arrayName(5, 4)

arrayName is the name of your array

ARRAYS
Hold a range (or is onlyvalues 1D Arrays
set) of about
Today
Basically a set of variables
Your arrays will mainly be 1 or 2 dimensions

arrayName(5)

arrayName(5)

arrayName(5, 4)

arrayName is the name of your array

DECLARING ARRAYS
The same rules apply to arrays as to variables
 Disposable, local or global? – Declare in the right place
 Must specify a data type

Also, need to specify the size of the array
 The “size” is the number of elements in the array

Public Sub DescriptiveStats()

5 stock prices

Dim stockPrices(5) As Double
Dim stockRet(4) As Double
End Sub

4 stock returns

DECLARING ARRAYS

5 stock prices
4 stock returns
The same rules apply to arrays as to variables
 Disposable, local or global? – Declare in the right place
 Must specify a data type

Also, need to specify the size of the array
 The “size” is the number of elements in the array


5 stock prices

Dim stockPrices(5) As Double
Dim stockRet(4) As Double
End Sub

4 stock returns

DECLARING ARRAYS
Many times we don’t know the number of
elements that will be in the array.
So, first declare them empty (disposable, local or
global): Dim stockPrices() As Double
For example,
Dim stockRet() As Double

these are local

End Sub

General format
for declaration

arrayName() As DataType
arrayName:= the name of the array
DataType:= Integer, Double, String…

DECLARING ARRAYS
After the size of the array is know, re-declare it
inside a procedure
Dim stockPrices() As Double
Dim stockRet() As Double
Dim nDays As Integer

nDays = Combobox1.value
ReDim stockPrices(nDays) As Double
ReDim stockRet(nDays-1) As Double

End Sub

Arrays will most likely
need to be local or
global

User selects number
of days from a
ComboBox on the
userform
Redim both arrays
using the variable

DECLARING ARRAYS
After the size of the array is know, re-declare it
inside a procedure

General format for
re-declaration
ReDim arrayName(n) As DataType
n:= the number of elements in the array

ARRAYS
VBA counts elements of arrays starting with 0
For example,
 This array is named StockPrices
 It has 5 elements (i.e., 5 stock prices)

Count
0
1

StockPrices(1)

2
3

StockPrices(2)
StockPrices(3)

4

StockPrices(4)

StockPrices(0)

ARRAYS
To force VBA to count from 1
 Use Option Base 1 at the top of each module

Count
1
2

StockPrices(2)

3
4

StockPrices(3)
StockPrices(4)

5

StockPrices(5)

StockPrices(1)

BEFORE ARRAYS…
We had to declare multiple variables like this:

And assign values like this:

WITH ARRAYS…
We can declare an array like this:

And assign values like this:

FILLING ARRAYS FROM CELLS OR RANGES

A 1D array and a
single For-Next
loop so this is only
for Stock 1

i=1
i=2
i=3
i=4
i=5
.
.
.
i=9

FILLING ARRAYS FROM CELLS OR RANGES

Cells(1,1)

i=1
i=2
i=3
i=4
i=5
.
.
.
i=9

A 1D array and a
single For-Next
loop so this is only
for Stock 1

Range Named
“Prices”

FILLING ARRAYS IN GENERAL
You can ‘fill’ arrays with values from…
 Cells
 Ranges
 Userform controls
 Other variables or arrays
 Using equations (e.g., calculate returns)

OUTPUTTING ARRAYS TO CELLS OR RANGES

i=1

i=2

i=3

i=4

i=5

**This is assuming we have assigned each element of the array weights() a value**

OUTPUTTING ARRAYS TO CELLS OR RANGES

Range Named
“StockWeights”

Cells(1,1)

i=1

i=2

i=3

i=4

i=5

**This is assuming we have assigned each element of the array weights() a value**

OUTPUTTING ARRAYS IN GENERAL
You can ‘output’ the value of arrays to…
 Cells
 Ranges
 Userform controls
 Other variables or arrays

EXERCISE 4A. WRITE A FOR LOOP
 LoopExercise4A in Module1

Declare an array for stock returns
Use that array in a For-Loop to rewrite this code.
 Remember to declare your counter!
Public Sub LoopExercise4A()
stockRet1 = Cells(4, 6).Value
End Sub

EXERCISE 4B. WRITE A FOR LOOP
Now, instead of using cell references use range
references to assign the array values:
Public Sub LoopExercise4A()
End Sub

Public Sub LoopExercise4B()
stockRet1 = Range(“Returns”).Cells(1, 1)
End Sub

Exercise 4A

Exercise 4B

Check your array has correct values by either:
 Outputting the array values to different cells (any cells)
 Or by using a message box
 Or by stepping through your code and checking the value
of each array element.

WRITE SUMS USING LOOPS & ARRAYS
sum = stockPrice(1) + stockPrice(2) + stockPrice(3)


i=1

i = 1 sum = stockPrice(1)


i=1

i=2

i = 2 sum = sum + stockPrice(2)


i=1

i=2

i=3



i=1

i=2

i=3

sum = 0

Make sure the
sum starts at 0

EXERCISE 5. WRITE A FOR LOOP
 LoopExercise4B in Module1

Find the sum of the 3 stock returns you assigned to
an array in Exercise 4B using a For-Next loop.
Check your sum with a message box. If you get the
following result, you are correct:

LEARNING OUTCOMES
 You are ready to move on when:
 LO21: You can use loops and concatenation to assign values to
controls on a userform or assign cells, ranges or 1D arrays
values from userform controls.
 LO22: You can describe what it means to generalise code. You
can also determine when loops should be generalised and how
to do so within your code.
 LO23: You can define what a nested loop is. You can also
construct basic nested loops to output values to cells or ranges.
Lastly, given a nested loop you can determine the result.
 LO24: You can describe the difference between a 1D and 2D
array. You can also declare an array with the correct number of
elements, in the correct location within your code and with the
correct data type. In addition, you understand when to declare
an array empty and how to use the ReDim statement.
 LO25: You can assign values to a 1D array as well as assign the
values of a 1D array to cells, a range or userform controls.

MA3696 Lecture 5

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MA3696 Lecture 5