A variable (X) is declared as an integer Data Type, meaning it can only accept numeric values

The Text Box is named BoxContents

The Variable X is assigned the value of the Height property of BoxContents (Text Box)

The Text property of BoxContents consists of a literal and the value of the variable X

The Text in BoxContents is also printed on the form

Before Project Execution

During Project Execution

Additional Instructions

Make the Text Box blank once the contents have been printed

Notify the user that the Text Box is blank

Add this Code to the End of the Sub-Procedure

BoxContents.Text =“”‘Empties whatever is in the text box

Print “The Text Box (BoxContents) is now blank”‘Prints this message on the form

Operators and Operands in Expressions

An Operand can be thought of as something that has a value

An Operator is the symbol of an operation carried out on at least 2 operands

There are 3 main types of Operator in VB, which take the following Order of Precedence:

- Arithmetic Operators- Relational (Comparison) Operators

- Logical Operators

Expressions

An Expression is a Visual Basic Action

There are 2 types of Expression in VB:

- Simple- Compound

An expression is formed by combining Operators and Operands in a meaningful way

The purpose of an expression is to perform a calculation and produce a result, or to cause some action to occur

Simple Expression: (A+B)

Compound Expression: An expression with more than 1 OPERATION is called a Compound Expression

[(A+B)*(C-D)]

(A, B, C, D) are the Operands(*, +, -) are the Operators

Each of these Operator Symbols represents an Operation

Arithmetic Operators

The hierarchy of operations, or order of precedence, in arithmetic expressions from the highest to the lowest is:

[1] Exponentiation: ^ (2 ^ 3 = 8)[2] Multiplication and Division: * /[3] Addition and Subtraction: + --

Example

3 + 4 * 2 = 11However, the order of evaluation can be changed by using

parentheses: ()(3 + 4) * 2 = 14

If one set of parentheses are used inside another set, the parentheses are referred to as nested

((3 + 3) / 3) * 4 = 8

(((4 + 3 * 4) / 2) * 4 + (4 + 10 / 2 - 3)) = ?

Nested

What Data Types would be assigned to the Variable X as a result of each of the following Operations

(2 + 4) (integer + integer) = integer/Long (2 - 4) (integer - integer) = integer/Long (2 * 4) (integer * integer) = integer/Long (2 / 4) (integer / integer) = Single/Double

(Two + Four) (string + string) = string (TwoFour)

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

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

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

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

CInt Function

Dim X As IntegerX = CInt(Text1.Text)

Print X

Dim X As Integer, Y As IntegerY = CInt(X) * 2

Print Y

CInt(“12”) the brackets are by default - 12CInt(“Twelve”) - Error

CInt(Text1.Text) - the value of the Text in Text1, if it is valid

cHours = 12.2

cPayRate = 5

cTotalPay = ?

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

Using the Val Function and the CCur Function, after multiplication, returns the value of 61

Hours.Text = 12.2

PayRate.Text = 5

However, if the value of Hours.Text = 12.2’

How would the Functions handle it?

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

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

Operand

Operator Expression Statement

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

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 statementsSELECT CASE statements

Program Statements

Program Statements

Program Statements

Program Statements

Evaluate an

Expression

Outcome A Outcome B

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] ThenAction/Statements

ElseAction/Statements

End If

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)

The test of an If statement is based on a condition

To form conditions, Relational(Comparison) 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> greater than

< less than= equal to

<> not equal to>= greater than or equal to

<= less than or equal to

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 stringsnumeric values compared with numeric values

whether a variable, constant, property of an object, or arithmetic expression

Dim Num1 as Integer

If Num1 > 10 ThenPrint “Num1 is greater than 10”

End If

If Num1 > 10 ThenPrint “Num1 is greater than 10”

ElsePrint “Num1 is less than 10”

End If

Val(Text1.Text)

Val(Text1.Text)

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

If..Then..Else statement syntax:

If [Condition/Expression] ThenAction/Statements

ElseIf [Condition/Expression] ThenAction/Statements

ElseAction/Statements

End If

Dim Temperature As Single

If Temperature <= 0 ThenPrint “Freezing”

ElseIf Temperature >= 30 ThenPrint “Hot”

ElsePrint “Moderate”

End If

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

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’:

ANDOR

NOT

Compound conditions/expressions are created using Logical Operators

Use compound conditions/expressions to test more than

one condition

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

Dim StudentName As StringDim Age As Integer

If StudentName = “Dave” AND Age >= 23 Then

If StudentName = “Dave” OR Age >= 23 Then

If StudentName = “Dave” AND NOT Age <= 23 Then

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

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

Nested If..Then statement syntax: (nested in the Then clause)

If [Condition/Expression] ThenIf [Condition/Expression] Then

Action/StatementsElse

Action/StatementsEnd If

ElseAction/Statements

End If

Nested If..Then statement syntax: (nested in the Else clause)

If [Condition/Expression] ThenAction/Statements

ElseIf [Condition/Expression] Then

Action/StatementsElse

Action/StatementsEnd If

End If

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

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, andLOGICAL OPERATORS

If..Then statements must be carefully structured as there is a definite order in which the conditions are tested

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)

Private Sub Command1_Click

If Option1.Value = True ThenPrint “Option1 Selected”

ElseIf Option2.Value = True ThenPrint “Option2 Selected”

ElseIf Option3.Value = True ThenPrint “Option3 Selected”

ElseIf Option4.Value = True ThenPrint “Option4 Selected”

ElsePrint “No Option Selected, Please Select Option”

End If

End Sub

Private Sub Command1_Click

If Check1.Value = 1 ThenPrint “Check1 Selected”

ElseIf Check2.Value = 1 ThenPrint “Check2 Selected”

ElseIf Check3.Value = 1 ThenPrint “Check3 Selected”

ElseIf Check4.Value = 1 ThenPrint “Check4 Selected”

ElsePrint “Nothing Checked”

End If

End Sub

Comparing Numeric Values

If Val(Text1.Text) = MaxPrice Then

(Is the current numeric value stored in the Text property of Text1 equal to the value stored in MaxPrice)

Even though an equal sign (=) means replacement in an assignment statement, in a relation test (using relational

operators) an equal sign is used to test for equality

Comparing Strings

String variables can be compared to other string variables or ‘string literals’ enclosed in quotation marks

The comparison begins with the Left-Most character and proceeds one character at a time from left to right

Each character is compared in the strings, and as soon as one is less than another the comparison is terminated and the string with the lower ranking character is judged less than the other

The determination of which character is less than other is based on the code used to store characters internally in the

computer

ASCII code (American Standard Code for Information Interchange) has an established order called the collating sequence, for all letters, numbers, and special characters

All numeric digits are less than all letters

Comparing the Text Property of Text Boxes

The Text Property can behave like a Variant, a String, a Number

A numeric expression/calculation on a Text Property can be forced by using the Val function

Testing for Boolean (True/False)

If X = True Then…. is equivalent to:If X Then….

Boolean Variables hold the value ‘0’ when False, and ‘-1’ when True

Any variable can be tested for ‘True’/‘False’

VB considers any numeric variable with a value of ‘0’ to be False, any other value will evaluate True

The variable or expression is referred to as an ‘implied condition’

iCounter = 10

If iCounter = 10 Then...

If iCounter Then...

Comparing Uppercase and Lowercase Characters

When comparing strings, the case of the characters is important

An Uppercase character is not equal to a Lowercase character

By using the String Function Ucase or Lcase, the Uppercase or Lowercase equivalent of a string can be compared

Ucase(string)Lcase(string)

Text1.Text Ucase(Text1.Text) Lcase(Text1.Text)

User types in Basic

BASIC basic

If Ucase(Text1.Text) = “BASIC” ThenPrint “Hello”

End If

When the text of Text1 is converted to Uppercase, it must be compared to an Uppercase ‘Literal’ (BASIC), if it is to

evaluate True

Select Case Statements (Case Structure)

A Select Case statement executes one of several groups of statements, depending on the value of an expression

An expression is selected and tested against a number of possible cases

The expression to be tested is usually a variable or object property

There is no limit to the number of statements that can follow a Case statement

If any of these cases match the value of the expression, the statements that follow are executed

Select Case statement syntax:

Select Case [Expression]Case [Expression Value/Constant List]

StatementsCase [Expression Value]

StatementsCase [Expression Value]

StatementsCase Else

StatementsEnd Select

The [Expression Value/Constant List] is the value that is required to be matched, and can be of the following types:

numeric or string type variable or constanta range of values

a relational conditionor a combination of these

To test a single variable or expression for multiple values, the Case Structure provides a flexible and powerful solution

Any program decisions that can be coded with a Case Structure can also be coded with Nested If Statements, but

usually the Case structure is simpler and clearer

When using a Relational Operator the word Is must be usedCase Is >= 100

To indicate a Range of Constants, use the word ToCase 25 To 90

To test for a String Value, quotation marks must be included around the literals

Case “Visual Basic”

In using Strings, the case(Upper/Lower) of the characters must be exact between the expression being tested and the

[Expression Value/Constant List] Select Case Ucase(Text1.Text)

Case “VISUAL BASIC”

A combination of Relational/Logical Operators, using Variables and ConstantsCase Is >= 10 AND Num1 <= 20

Although the Case Else clause is optional, generally it will be included in the Select Case statements

The statements coded underneath Case Else will execute only if none of the other Case Conditions is matched

The Case Else clause will provide checking for any invalid or unforeseen values of the expression being tested

If the Case Else clause is omitted and none of the Case Conditions is True, the program will continue execution at the

statement following the End Select

If more than one Case value is matched by the expression, only the statements in the first Case clause will be executed,

identifying a definite Hierarchy

Testing Option Buttons using the Case Structure

The Case Structure is ideal for testing which Option Button is selected