Val Function A Function performs an action and returns a value The expression to operate upon, known as the argument, (or multiple arguments), must be enclosed in parentheses Val an abbreviation for value Val(ExpressionToConvert) The expression that - PowerPoint PPT Presentation

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Val Function A Function performs an action and returns a value The expression to operate upon, known as the argument, (or multiple arguments), must be enclosed in parentheses Val an abbreviation for value Val(ExpressionToConvert) The expression that

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Title: Val Function A Function performs an action and returns a value The expression to operate upon, known as the argument, (or multiple arguments), must be enclosed in parentheses Val an abbreviation for value Val(ExpressionToConvert) The expression that


1
Val Function A Function performs an action and
returns a value The expression to operate upon,
known as the argument, (or multiple arguments),
must be enclosed in parentheses Val an
abbreviation for value Val(ExpressionToConvert)
The expression that is converted, can be the
Property of a Control, a Variable, or a
Constant
2
The Val Function returns (produces) a value that
can be used as a part of a statement, such as an
assignment statement iQuantity
Val(txtQuantity.Text) The Val Function converts
an argument to numeric, by beginning at the
Left-Most Character If that character is a
numeric digit, decimal point, or sign, Val
converts the character to numeric and moves to
the next character. As soon as a non-numeric
character is found, the operation stops
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Conversion Function The Conversion Function
checks if the value stored in the Property of a
Control or a Variable is of a specific Data Type
required in the execution of a statement(s), and
if not the Conversion Function will return a
Run-Time Error Message The Text in Text Boxes
is treated as a String, however in performing
Arithmetic Operations (such as / -),
numeric values are required in the Text property
of the Text Boxes
4
VB Conversion Functions CInt - Converts a value
to an Integer CLng - Converts a value to a Long
Integer CSng - Converts a value to a Single
Precision number CDbl - Converts a value to a
Double Precision nember CCur - Converts a value
to Currency CStr - Converts a value to a String
CVar - Converts a value to a Variant
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CInt Function Dim X As Integer X
CInt(Text1.Text) Print X Dim X As Integer, Y As
Integer Y CInt(X) 2 Print Y CInt(12) the
brackets are by default - 12 CInt(Twelve) -
Error CInt(Text1.Text) - the value of the Text in
Text1, if it is valid
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cHours 12.2 cPayRate 5 cTotalPay ?
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In the Sample code the Val Function is replaced
by the CCur Function
The value stored in the Text Property of the
Hours text box is converted from a String to
Currency and the value is assigned to the
Variable cHours as a Currency Data Type If the
value in the Text Property is not consistent with
the Currency Data Type, then a Run-Time Error
will occur and the program will stop executing
10
Hours.Text 12.2
PayRate.Text 5
Using the Val Function and the CCur Function,
after multiplication, returns the value of 61
However, if the value of Hours.Text 12.2 How
would the Functions handle it?
11
The Val Function will convert the value stored in
the Property of the control, to a numeric value,
before assigning it as the value of the variable
for use in an Arithmetic Calculation The
Conversion Function checks if the value stored in
the Property of a Control is of a specific Data
Type required in the execution of a statement(s)
(numeric for the purpose of calculation), and if
not the Conversion Function will return a
Run-Time Error Message
12
Basic Elements of Programming A VB program is
built from statements, statements from
expressions, expressions from operators and
operands, and operands from variables/constants
and the properties of objects
Operand
Operator
Expression
Statement
Operand
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Programming Constructs VB code is generally
comprised of combinations of the following
program statements Sequence Consisting of a
number of instructions which are processed in
sequence Selection Consisting of branches in
the VB program, containing different instructions
which are processed depending on the results of
certain tested conditions Iteration
Consisting of groups of statements which are
repeatedly executed until a certain tested
condition is satisfied
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Selection (Branching Constructs in VB) Branching
constructs are used to control program flow A
Condition/Expression is evaluated, and the result
determines which statements the program
executes There are 2 main types of Branching
Construct in VB IF statements SELECT CASE
statements
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Program Statements
Program Statements
Evaluate an Expression
Outcome A
Outcome B
Program Statements
Program Statements
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If Statements Projects can take one action or
another, based on a condition Make a decision
and take alternate courses of action based on the
outcome
If..Then statement syntax If
Condition/Expression Then Action/Statements Els
e Action/Statements End If
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The word Then must appear on the same line as
If Else and End If must appear on separate
lines The statements underneath the Then and
Else clause are indented for readability and
clarity (always indent code, especially with If
statements, the indentation helps to visualise
the intended logic and saves on project debugging
time) If..Then statements are generally used in
conjunction with the Relational (Comparison)
Operators These Relational (Comparison)
Operators are used to compare expressions, and
return a result of either True or False (Boolean
Data Type)
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The test of an If statement is based on a
condition To form conditions, Relational(Comparis
on) Operators are used, resulting in an outcome
being either True or False (Boolean Data
Type) There are 6 Relational(Comparison)
Operators in VB Order of Precedence of
Relational Operators gt greater than lt less
than equal to ltgt not equal to gt greater
than or equal to lt less than or equal to
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Conditions can be formed with - numeric
variables and constants - string variables and
constants - object properties, and - arithmetic
expressions However, comparisons have to be made
on like data types strings compared to
strings numeric values compared with numeric
values whether a variable, constant, property of
an object, or arithmetic expression
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Dim Num1 as Integer If Num1 gt 10 Then Print
Num1 is greater than 10 End If If Num1 gt 10
Then Print Num1 is greater than 10 Else Print
Num1 is less than 10 End If
Val(Text1.Text)
Val(Text1.Text)
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Multiple Branching The logic of a program may
require that there be more than one branch in the
program In this case the ElseIf keyword(clause)
is added to the If..Then statement to increase
flexibility An infinite amount of ElseIf
statements can be included into the If..Then
statement
22
If..Then..Else statement syntax If
Condition/Expression Then Action/Statements Els
eIf Condition/Expression Then Action/Statements
Else Action/Statements End If
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Dim Temperature As Single If Temperature lt 0
Then Print Freezing ElseIf Temperature gt 30
Then Print Hot Else Print Moderate End If
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If..Then..Else statements have a definite
hierarchy The order of an If..Then..Else
statement is important, due to the fact that if
the first line of the If..Then..Else statement is
True, then none of the other ElseIf statements
will be processed/executed If..Then statements
can be given greater flexibility in 2 main
ways 1 Using Logical Operators 2
Nesting If..Then statements
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Logical Operators Logical Operators should be
used when a limited number of conditions are to
be tested The 3 most commonly used Logical
Operators in VB are in Order of
Precedence AND OR NOT Compound
conditions/expressions are created using Logical
Operators Use compound conditions/expressions
to test more than one condition
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AND Both conditions must be true for the entire
condition to be true OR If one condition or
both conditions are true, the entire condition is
true NOT Reverses the condition, so that a true
condition will evaluate false and vice versa The
use of parentheses can change the Order of
Precedence of these Logical Operators Always
plan the use of Logical Operators, as their use
can often involve confusing logic
27
Dim StudentName As String Dim Age As
Integer If StudentName Dave AND Age gt 23
Then If StudentName Dave OR Age gt 23 Then
If StudentName Dave AND NOT Age lt 23 Then
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Logical Operator Guidelines Result Expression1
Logical Operator Expression2 If Expression1 AND
Expression2 Then Result True
True True True False False
False True False
False False False If
Expression1 OR Expression2 Then Result
True True True True
False True False True
True False False False
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Nesting If..Then Statements If..Then statements
that contain additional If..Then statements are
said to be nested If statements If more than one
Expression has to be checked in the program,
If..Then statements can be nested You may nest
If..Then statements in both the Then and Else
portion of the statement syntax You can continue
to nest If..Then statements within If..Then
statements as long as each If has an End If
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Nested If..Then statement syntax
(nested in the Then clause) If
Condition/Expression Then If
Condition/Expression Then Action/Statements E
lse Action/Statements End If Else Action/State
ments End If
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Nested If..Then statement syntax
(nested in the Else clause) If
Condition/Expression Then Action/Statements Els
e If Condition/Expression Then Action/Stateme
nts Else Action/Statements End If End If
32
The first If..Then statement which the program
encounters is called the OUTER If..Then
statement Any If..Then statements placed within
the first statement are called INNER If..Then
statements INNER If..Then statements are only
processed when the OUTER If..Then statement is
True Nested If..Then statements have to be
carefully structured There is a definite
Order/Hierarchy in relation to the way in which
they are processed
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If..Then statements If..Then statements check
the value of an expression and carry out
different instructions based on the
result If..Then statements are a useful and
flexible method of allowing a program to branch
into different directions If..Then statements
become more powerful and flexible through the use
of the ELSEIF clause NESTED IF..THEN statements,
and LOGICAL OPERATORS If..Then statements must
be carefully structured as there is a definite
order in which the conditions are tested
37
Using If..Then statements with Option Buttons and
Check Boxes In using If..Then statements, with
Option Buttons and Check Boxes, no action should
be taken in the click events for these
controls Code should be written in the
Click_Event of a Command Button, where certain
actions will be performed when the command button
is clicked, relating to the selection of an
option button (value property of the option
button), or the checking of a check box (value
property of the check box)
38
Private Sub Command1_Click If Option1.Value
True Then Print Option1 Selected ElseIf
Option2.Value True Then Print Option2
Selected ElseIf Option3.Value True Then Print
Option3 Selected ElseIf Option4.Value True
Then Print Option4 Selected Else Print No
Option Selected, Please Select Option End
If End Sub
39
Private Sub Command1_Click If Check1.Value 1
Then Print Check1 Selected ElseIf Check2.Value
1 Then Print Check2 Selected ElseIf
Check3.Value 1 Then Print Check3 Selected
ElseIf Check4.Value 1 Then Print Check4
Selected Else Print Nothing Checked End
If End Sub
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