IE 212: Computational Methods for
Industrial Engineering
Lecture Notes #6:
Function Procedures & Arrays
Saeed Ghanbartehrani
Summer 2015
Overview

Organizing Sub Procedures

Creating Function Procedures

Methods to Pass Variables in Sub and Function Procedures

Public and Private Procedures

Using Arrays in Excel VBA

Summary
2
Organizing Sub Procedures

You should group various actions into several smaller sub
procedures rather than having one large sub procedure in
which the entire program is written
– Allows for programs to run more efficiently
– Promotes code reusability

The ideal module structure for your program is to have one
Main() sub procedure from which other sub procedures are
called
– This Main macro will usually be assigned to a “Start” button on the
“Welcome” sheet

To call another sub procedure, we use the command Call
followed by the sub procedure name
3
Organizing Sub Procedures (cont.)

For example, consider three different sub procedures, called
GetInput(), Calculations(), and DisplayResults()

We can then call these three sub procedures from the Main()
sub procedure as follows
Sub Main()
Call GetInput
Call Calculations
Call DisplayResults
End Sub

You can also call other sub procedures from these three sub
procedures
4
Function Procedures

A function procedure is a type of procedure that can take
arguments and execute a series of statements

A function procedure differs from a sub procedure in that
– It is invoked through its name
– It returns a single value

Critical elements when writing a function procedure
– The name of the function
– The type of the function
5
Function Procedures (cont.)

Syntax of a function procedure
Function name ([arglist])
[statements]
[name = expression]
[Exit Function]
[statements]
[name = expression]
End Function

A function procedure can be called from any sub procedure
or any other function procedure
Function FunctionName()
….
End Function
6
Function Procedures (cont.)

To illustrate the proper use of a function in Excel VBA, we
will use an example where the sum of two values is
calculated
– We will use AddTwoNumbers as the name of the function
7
Function Procedures (cont.)

The function itself is quite simple in this case

To return a value from a function in Excel VBA, you should
assign a value to the name of the function procedure

The variables x and y in this example do not need to be
declared
– They are the variables used throughout the function procedure
8
Function Procedures (cont.)

The variables x and y in the function AddTwoNumbers will
assume the respective data types assigned to a and b
– If we had defined the function AddTwoNumbers with data types in
the argument, we would be restricted to only passing variables of that
data type
– Function AddTwoNumbers(x As Integer, y As Integer)

Notice also that the variable names used as arguments
when the function is called and the variable names used in
the function procedure statement do not need to be the
same
– a and b in Sub procedure
– x and y in Function procedure
9
Methods to Pass Variables

There are two methods to pass variables in sub procedures
and function procedures
– By reference (default)
– By value

Passing a value by reference implies that the procedure (or
function) can access and possibly modify the original value
assigned to the variable

Passing by value provides a copy of the value of the
variable for the procedure or function to use
– Therefore, the original value of the variable remains intact
10
Methods to Pass Variables (cont.)

To pass a variable by value, we must use the keyword
ByVal when defining the arguments that the function will
take
Function AddTwoNumbers(ByVal x, ByVal y)
AddTwoNumbers = x + y
End Function

Alternatively, a variable can be passed by value by
enclosing it in parentheses when the sub procedure or
function is called
Call Multiply((i), j)  Sub procedure
result = Multiply((a), (b))  Function procedure
11
Public and Private Procedures

The scope of a sub procedure, like a variable, can also be
defined as Public or Private

A private sub procedure is declared by putting the word
Private before the Sub statement
– Private sub procedures can only be called from procedures in the
same module
– Private sub procedures are not listed when you try to run a macro in
Excel

A public sub procedure can be called from any other
procedure
– The word Public can be put in front of the Sub statement, or the Sub
statement can be written without a preceding statement
12
Using Arrays in Excel VBA
13
Introduction to Arrays in Excel VBA

Arrays store series of data elements that can be
manipulated or referred to later
– Arrays are very useful when we need to perform the same operation
(or a series of operations) on a group of values
– Arrays may also make programs more compact (and possibly more
efficient)
 For example, if we know a program’s output will be 3 integer variables,
we can store these values in an integer array of size 3

The set of data elements stored in an array must all be of
the same data type
14
Declaring Arrays

To declare an array, the variable declaration keywords Dim,
Private, or Public can be used

VBA will recognize a variable as an array and not a scalar
variable because a set of parentheses (and, in some cases,
the size of the array) is included in the variable declaration
– Dim stdNames(10) As String
– Dim stdGrades() As Integers

This is how the one-dimensional array tempData,
containing 10 elements of data type Double, is declared
– Dim tempData(9) As Double
15
Declaring Arrays (cont.)

For a one-dimensional array, a single number is all that is
necessary to specify the size

To declare multi-dimensional arrays, you need to specify
the size of each dimension (i.e., rows and columns),
separated by a comma
– Dim data(2, 3) As Double
16
Arrays’ Indices

You can refer to the individual elements in an array using an
index value
– When an array is declared in Excel VBA, a default index is assigned
to each element

The default index of the first element in a one-dimensional
array is 0

The default index of the first element in a two-dimensional
array is 0,0
17
Arrays’ Indices (cont.)

Examples
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18
Arrays’ Indices (cont.)

You can instruct Excel VBA to change the default index
values of all arrays in your module with the instruction
Option Base 1
– One dimensional arrays will begin at 1
– Two-dimensional arrays will begin at 1,1
Option Base 1
Dim data(10) As Double, results(12) As Double

If you want to keep the default initial index as 0 but would
like a specific array to start with a different index, you can
specify the starting index value in the array declaration
– Dim data(1 To 10) As Long, results(12) As Double
– Dim matrix(1 To 20, 1 To 10) As Double
19
Arrays’ Indices (cont.)

In the last case, just be aware of the size of your array
– Dim results(2 to 13) As Double
– size = upper index bound – lower index bound + 1

Whichever initial index value is chosen, it should be
coordinated with the counter variable used in For…Next
loops
For i = 1 To 13
results(i) = value
Next i
20
Arrays’ Indices (cont.)

LBound Function
– Returns a Long containing the smallest available subscript for the
indicated dimension of an array
– Syntax  LBound(arrayname [, dimension])

UBound Function
– Returns a Long containing the largest available subscript for the
indicated dimension of an array
– Syntax  UBound(arrayname [, dimension])
Dim A(1 To 100, 0 To 3) as Integer
LBound(A, 1)
UBound(A, 1)
LBound(A, 2)
21
UBound(A, 2)
Populating Arrays with Values

To assign a value of a specific element of the array, we
use the index of the element
– For example, to assign a value of 10.5 to the third member of array
data(9), we would type
 data(2) = 10.5

To set multiple values of an array, it is more practical to
use a For…Next loop with a counter variable

For example, to set each element in the array data(9)
equal to its index number, we would type
For i = LBound(data) To UBound(data)
data(i) = i
Next i
22
Populating Arrays with Values (cont.)

To assign values to the elements of a multi-dimensional
array or to search for a value, use nested For…Next loops
with different counter variables

For example, to set the value of each element in the twodimensional array data(4, 9) equal to the product of its
indices, you would do the following:
0
0
0
0
0
0
0
0
0
0
0
1
2
3
4
5
6
7
8
9
0
2
4
6
8
10 12 14 16 18
0
3
6
9
12 15 18 21 24 27
0
4
8
12 16 20 24 28 32 36
23
Dynamic Arrays

If you are not sure about the size of an array at declaration
time, you can use a dynamic array declaration
– For example, sometimes we expect the user to tell our application
how many elements the array should have

When declaring a dynamic array, the array size is not
specified and the parentheses are left empty
– Dim input() As Double

However, before this array or any of its elements is used, we
must (eventually) know its size and declare it accordingly
24
Dynamic Arrays (cont.)

To set the size of a dynamic array at some later point in the
code, we use the ReDim statement

The ReDim statement can also be used to set or change the
number of dimensions and the indexing bounds
– Suppose we want to ask the user to provide input values, which we
will store in our array input
25
Dynamic Arrays (cont.)

If you want to change the size of a dynamic array but do not
want to reset its values, then use the statement ReDim
Preserve
– Suppose we have a dynamic array of size 9 which has already been
populated with values and we need to add one more value

To keep the current values in the array but add one more
element, we type
ReDim Preserve input(10)
input(10) = InputBox(“Please enter new value.”)
26
Summary

To call another sub procedure, use the command Call
followed by the sub procedure name

Function procedures are similar to sub procedures and
follow this basic structure:
Function FunctionName()
….
End Function
27
Summary (cont.)

To pass a variable in Excel VBA, you should insert the
variable as an argument/parameter of the function when it is
called

A sub procedure, like a variable, can also be defined as
Public or Private
28
Summary (cont.)

Arrays store series of data that we can manipulate or refer to
later

To define an array, use the Dim, Private, or Public variable
declarations
– For a one-dimensional array, we just need a single number to specify
the size
– To define multi-dimensional arrays, we must specify the size of each
dimension, separated by a comma

The default initial index value of arrays in VBA is 0

To change the initial index value of all arrays in our module
to 1, type Option Base 1 at the top of the module
29
Summary (cont.)

To set the size of a dynamic array at some later point in the
code, use the ReDim statement

The ReDim Preserve statement retains any previously
assigned element values
– Only works with dynamic arrays
30