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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.

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Presentation on theme: "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."— Presentation transcript:

1 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


3 Before Project Execution During Project Execution

4 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

5 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

6 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

7 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

8 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 = 11 However, the order of evaluation can be changed by using parentheses: () (3 + 4) * 2 = 14

9 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

10 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)





15 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

16 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

17 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

18 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

19 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



22 cHours = 12.2 cPayRate = 5 cTotalPay = ?

23 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

24 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?

25 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

26 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 OperatorExpressionStatement

27 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

28 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

29 Program Statements Evaluate an Expression Outcome AOutcome B

30 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 Else Action/Statements End If

31 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)

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

33 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

34 Dim Num1 as Integer If Num1 > 10 Then Print “Num1 is greater than 10” End If If Num1 > 10 Then Print “Num1 is greater than 10” Else Print “Num1 is less than 10” End If Val(Text1.Text)

35 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

36 If..Then..Else statement syntax: If [Condition/Expression] Then Action/Statements ElseIf [Condition/Expression] Then Action/Statements Else Action/Statements End If

37 Dim Temperature As Single If Temperature = 30 Then Print “Hot” Else Print “Moderate” End If

38 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

39 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

40 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

41 Dim StudentName As String Dim 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

42 Logical Operator Guidelines Result = Expression1 Logical Operator Expression2 If Expression1AND Expression2Then Result True TrueTrue True False False False True False False False False If Expression1OR Expression2Then Result True TrueTrue True False True False True True False False False

43 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

44 Nested If..Then statement syntax: (nested in the Then clause) If [Condition/Expression] Then If [Condition/Expression] Then Action/Statements Else Action/Statements End If Else Action/Statements End If

45 Nested If..Then statement syntax: (nested in the Else clause) If [Condition/Expression] Then Action/Statements Else If [Condition/Expression] Then Action/Statements Else Action/Statements End If End If

46 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




50 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

51 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)

52 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

53 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

54 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

55 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

56 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

57 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...

58 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)

59 Text1.Text Ucase(Text1.Text) Lcase(Text1.Text) User types in Basic BASIC basic If Ucase(Text1.Text) = “BASIC” Then Print “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

60 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

61 Select Case statement syntax: Select Case [Expression] Case [Expression Value/Constant List] Statements Case [Expression Value] Statements Case [Expression Value] Statements Case Else Statements End Select

62 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 constant a range of values a relational condition or 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

63 When using a Relational Operator the word Is must be used Case Is >= 100 To indicate a Range of Constants, use the word To Case 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 Constants Case Is >= 10 AND Num1 <= 20

64 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


66 Testing Option Buttons using the Case Structure The Case Structure is ideal for testing which Option Button is selected

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