CIV 257- COMPUTER PROGRAMMING
Lecture 3
CIVIL AND GEOMATIC ENGINEERING
FT Okyere.
Scope of a Variables
 A variable's scope is determined by where you declare it.
 When you declare a variable within a procedure, only code
within that procedure can access or change the value of that
variable.
 It has local scope and is a procedure-level variable.
 If you declare a variable outside a procedure, you make it
recognizable to all the procedures in your script. This is a
script-level variable, and it has script-level scope.
Lifetime of Variables
 The lifetime of a variable depends on how long it exists.
 The lifetime of a script-level variable extends from the time
it is declared until the time the script is finished running.
 At procedure level, a variable exists only as long as you are in
the procedure.
 When the procedure exits, the variable is destroyed. Local
variables are ideal as temporary storage space when a
procedure is executing.
 You can have local variables of the same name in several
different procedures because each is recognized only by the
procedure in which it is declared.
Assigning Values to Variables
 Values are assigned to variables creating an expression as
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follows:
the variable is on the left side of the expression and the value
you want to assign to the variable is on the right.
For example:
B = 200
Speed1=20
t=+1 or t=t+1
Scalar Variables and Array Variables
 Much of the time, you only want to assign a single value to a
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variable you have declared.
A variable containing a single value is a scalar variable.
Other times, it is convenient to assign more than one related
value to a single variable.
Then you can create a variable that can contain a series of
values. This is called an array variable.
Array variables and scalar variables are declared in the same
way, except that the declaration of an array variable uses
parentheses ( ) following the variable name.
Array Variables
 single-dimension array containing 11 elements is declared:
 Dim A(10)
 Although the number shown in the parentheses is 10, all
arrays in VBScript are zero-based, so this array actually
contains 11 elements.
 E.g. Dimension an array to contain 12 elements.
 Dim arr1(11)
 You assign data to each of the elements of the array using an
index into the array.
Array Variables
 A(0) = 256
 A(1) = 324
 A(2) = 100
 ...
 A(10) = 55
 Similarly, the data can be retrieved from any element using
an index into the particular array element you want. For
example:
SomeVariable = A(8)
Array Variables
 VB program to add two vectors of same dimension
 3x1 +3x1
 Create 3 arrays
 Dim arr1(2)
 Dim arr2(2)
 Dim arr3(2)
 ‘assign values to the array
 Arr1(0)=txtarr11.text
 Arr1(1)=txtarr12.text
Array Variables- Example
 Arr1(2)=txtarr13.text
 Arr2(0)=txtarr21.text
 Arr2(1)=txtarr22.text
 Arr2(2)=txtarr23.text
 ‘Now lets add array elements
 Arr3(0)=arr1(0)+arr2(0)
 Arr3(1)=arr1(1)+arr2(1)
 Arr3(2)=arr1(2)+arr2(2)
similarly
Array Variables- Multidimensional
 You can declare multiple dimensions(UP TO 60 DIMENSIONS)
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by separating an array's size numbers in the parentheses with
commas.
In the following example, the MyTable variable is a twodimensional array consisting of 6 rows and 11 columns:
Dim MyTable(5, 10)
Remember zero indexing
You can also declare an array whose size changes during the time
your script is running.
This is called a dynamic array. The array is initially declared
within a procedure using
Dim MyArray()
ReDim AnotherArray()
Access Levels in Visual Basic
Public
Private
Protected
Protected Friend
Friend
 Public
 The Public (Visual Basic) keyword in the declaration statement
specifies that the elements can be accessed from code anywhere in
the same project, from other projects that reference the project,
and from any assembly built from the project.
 Public class classforall
 ‘the elements within are accessible from everywhere in the project and from
‘projects that reference this project
 End class
Access Levels in Visual Basic
 Private
 The Private (Visual Basic) keyword in the declaration
statement specifies that the elements can be accessed only
from within the same module, class, or structure.
Private x1 as integer ‘this is accessible form the within the
module and not without it
At module level dim statement works like private
 Protected
 The Protected (Visual Basic) keyword in the declaration
statement specifies that the elements can be accessed only
from within the same class, or from a class derived from
this class.
Access Levels in Visual Basic
 Friend
 The Friend (Visual Basic) keyword in the declaration
statement specifies that the elements can be accessed from
within the same assembly, but not from outside the
assembly.
 Protected Friend
 The Protected and Friend keywords together in the
declaration statement specify that the elements can be
accessed either from derived classes or from within the same
assembly, or both.
Public Class Form1
Protected t As String
Private Sub Button1_Click_1(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
End Sub
End Class
 Data Types -Visual Basic
 The following table shows the Visual Basic data types, their
supporting common language runtime types, their nominal
storage allocation, and their value ranges.
 Type Memory
VB Data
Allocation
Value Range
Double
8 bytes
-1.79769313486231570E+308 through
4.94065645841246544E-324
for negative values; 4.94065645841246544E-324 through
1.79769313486231570E+308
for positive values
Single
4 bytes
-3.4028235E+38 through -1.401298E-45 for negative
values; †
Integer
4 bytes
-2,147,483,648 through 2,147,483,647 (signed)
String
Depends on
platform
0 to approximately 2 billion Unicode characters
Boolean
Depends on
platform
True or False
Data types- VB
 Examples
 Double E.g. 2.3433434343 or -44.4
 Integer E.g. 342 or -78
 Long E.gVery large integer 2,147,483,648,000
 E.g. dim t as string= “characters make up a string”
 The variable t stores the string made up of c, h, a, r, a, c, t, e, r, s,
,m,a,k,e, ,u,p, ,a,
 ,s,t,r,I,n,g
 SPACES ARE CHARACTERS- TRY MSWORD COUNT!
Mathematical Operators
Mathematical Operators
 The arithmetic and concatenation operators have
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the order of precedence
described in the following section, and all have greater
precedence than the comparison,logical, and bitwise
operators.
The logical and bitwise operators have the order of
precedence
They have lower precedence than the arithmetic,
concatenation, and comparison operators.
Arithmetic and conc.>Comparison>logical
Operators with equal precedence are evaluated left to right
in the order in which they appear in the expression.
Mathematical Operators
 Exponentiation (^) Raises a number to the power of
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another number.
number ^ exponent
E.g. t= 2^3
t=8
Unary identity and negation (+, –) Multiplies two
numbers. -1*number
operand number
-6
+7
In mathematics, a unary operation is an operation with only one
operand
Mathematical Operators
 Multiplication and floating-point division (*, /) Divides
two numbers and retfloating-point result.
 E.g. t= 2*3
 T=6
 expression1 / expression2
 E.g. t=8/2
 t=4
Mathematical Operators
 Integer division (\)Divides two numbers and returns an
integer result.
 expression1 \ expression2
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Dim t As Integer
t=4\3
t=1
Modulus arithmetic (Mod) Divides two numbers and
returns only the remainder.
 number1 Mod number2
 E.g. t= 2 mod 9
 t=1
Mathematical Operators
 Addition and subtraction (+, –), string concatenation
(+) Adds two numbers or returns the
 positive value of a numeric expression. The Can also be used
to concatenate two string
 expressions.
 expression1 + expression2
 - or  + expression1
 E.g. t= 2+11
str=”The Garfield”+” Movie” <STRING CONCATENATION
str=” The Garfield Movie”
Comparison Operators
Operator
True if
False if
< (Less than)
expression1 < expression2
expression1 >= expression2
<= (Less than or equal to)
expression1 <= expression2
expression1 > expression2
> (Greater than)
expression1 > expression2
expression1 <= expression2
>= (Greater than or equal to)
expression1 >= expression2
expression1 < expression2
= (Equal to)
expression1 = expression2
expression1 <> expression2
<> (Not equal to)
expression1 <> expression2
expression1 = expression2
Comparison Operators
 The result of a comparison operation is a boolean datatype
True or false
 Example
 Dim testResult As Boolean
 testResult = 45 < 35
 testResult = 45 = 45
 testResult = 4 <> 3
 testResult = "5" > "4444"
Arithmetic Operators VBExample
1. Dim num1, num2, difference, product, quotient
As Single
2. num1 = TextBox1.Text
3. num2 = TextBox2.Text
4. sum=num1+num2
5. difference=num1-num2
6. product = num1 * num2
7. quotient=num1/num2
8. Label1.Text=sum
9. Label2.Text=difference
10. Label3.Text = product
Logical Operators
 Logical Operators
 Logical operators compare Boolean expressions and return a
Boolean result (True or
 False).
 Not Bitwise
Logical Operators
 Negation (Not)
Performs logical negation on a Boolean expression, or
bitwise negation on a numeric
expression.
result = Not expression
If expression is
True
False
 Example
The value of result is
False
True
Dim var As Boolean = Not (2 < 3)
Logical Operators
Conjunction (And, AndAlso)
Performs a logical conjunction on two Boolean
expressions, or a bitwise conjunction on
two numeric expressions.
result = expression1 And expression2
If expression1
is
True
True
False
False
And expression2
is
True
False
True
False
The value of
result is
True
False
False
False
Logical Operators
Inclusive disjunction (Or, OrElse)
Performs a logical disjunction on two Boolean
expressions, or a bitwise disjunction on two numeric
expressions.
result = expression1 Or expression2
If expression1 is
And expression2 is
The value of result is
True
True
True
True
False
True
False
True
True
False
False
False
Logical Operators
Exclusive disjunction (Xor)
Performs a logical exclusion on two Boolean expressions,
or a bitwise exclusion on two numeric expressions.
result = expression1 Xor expression2
For Boolean comparison, result is True if and only if
exactly one of expression1 and expression2 evaluates to True
If expression1 is
And expression2 is
The value of result is
True
True
False
True
False
True
False
True
True
False
False
False
Arithmetic, logical and comparison
operator Examples:
BODMAS with exponentiation and other operators
BEODMASCL
BRACKET EXPONENTIAL
OF DIVISION MULTIPLICATION
ADDITION SUBTRACTION
COMPARISON LOGICAL
1. ((1+3)-(2*4-1)/-1
2. ((5+3)-(2ˆ4-1)/(-1-1*4)
3. (1>2) XOR (3>4)
VB Control Structures
Repetition and Conditional Statements
Vb sYNTAX
If condition [ Then ]
[ statements ]
[ ElseIf elseifcondition [ Then ]
[ elseifstatements ] ]
[ Else
[ elsestatements ] ]
End If
VB Control Structures
If Statement
condition
A condition is required. That expression must evaluate to True
or False, or to a data type
that is implicitly convertible to Boolean (e.g. a>b).
Optional. One or more statements following If...Then that
are executed if condition
evaluates to True.
elseifcondition
Required if ElseIf is present. The expression must
evaluate to True or False, or to a data
type that is implicitly convertible to Boolean.
VB Control Structures
elseifstatements
Optional. One or more statements following
ElseIf...Then that are executed if
elseifcondition evaluates to True.
elsestatements
Optional. One or more statements that are executed if no
previous condition or
elseifcondition expression evaluates to True.
End If
VB Control Structures
Example
If i = 2 Then
g2 = i * 1000
ElseIf i = 4 Then
MsgBox("i=4")
End If
The appalling silence of good people
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