Introduction to Computing Dr. Nadeem A Khan

Lecture 19

Lecture 20 in Lab !

Functions

Functions ► General Format : Subroutine Sub SubprogrammeName (list of parameters) statements End Sub ► General Format : Functions Sub FunctionName (list of parameters) As datatype statements Function Name = expression End Function

Functions ► Examples: Function FtoC (t As Single) As Single FtoC = (5/9)*(t-32) End Function Function FirstName$ (nom As String) Dim firstSpace As Integer Rem Extract the first name from the full name nom Let firstSpace = Instr(nom, “ ”) FirstName$ = Left$(nom, firstSpace-1) End Function

Functions ► Using function in a program Sub Command1_Click Dim x As Single Picture1.Print FtoC(212) x = FtoC(32) Picture1.Print x x = FtoC(81+32) Picture1.Print x End Sub

Functions (Contd.) ► Result:

► Practice Problem Function Cider (g As Single, x As Single) As Single Cider=g*x End Function Sub DisplayNumOfGallons(galPerBu, apples As Single) Picture1.Cls Picture1.Print “You can make”; Cider(galPerBu, apples); Picture1.Print “gallons of cider.” End Sub Sub GetData (gallonsPerBushel As Single, apples As Single) Let gallonsPerBushel =3 Let apples =9 End Sub Functions (Contd.)

► Practice Problem Sub Command1_Click Rem How many gallons of apple cider can we make Dim gallonsPerBushel As Single, apples as Single Call GetData(gallonPerBushel, apples) Call DisplayNumOfGallons(gallonsPerBushel, apples) End Sub

Functions (Contd.) ► Practice Problem: Result You can make 27 gallons of cider

Private and Public ► Variables, Subroutines and Functions can be declared as Private or Public as well ► Read Section 2.4 (Scott Warner) Scope  Local  Module/Form-Level  Global

Modular Design ► Top-Down Design ► Structured Programming  Sequences  Decisions  Loops

Note: ► Read: Schneider (Section 4.2,4.3, 4.4) ► Read comments and do practice problems of these sections of these sections ► Attempt questions of Exercises

Conditions

Conditions: Examples ► ExpressionTrue/False 2 < 5? -5 > -2.5? 1 < 1? 1 = 1? 3.5 <= 3.5? -9 >= -35? -2 <> -3?

Conditions: Examples (Contd.) ► ExpressionTrue/False 2 < 5True -5 > -2.5False 1 < 1False 1 = 1True 3.5 <= 3.5True -9 >= -35True -2 <> -3True

Conditions: Examples (Contd.) ► ExpressionTrue/False “cat” < “dog”? “cart” < “cat”? “cat” < “catalog”? “9W” < “bat”? “Dog” < “cat” ? “Sales-99 <= “Sales-retail”?

Conditions: Examples (Contd.) ► For strings use the ANSI (or ASCI) table CharactersANSI(ASCI) Value CharactersANSI(ASCI) Value Digits (0-9)48-57 Upper Case (A-Z)65-90 Lower Case (a-z) ► Compare two strings character by character

Conditions: Examples (Contd.) ► ExpressionTrue/False “cat” < “dog”True “cart” < “cat”True “cat” < “catalog”True “9W” < “bat”True “Dog” < “cat” True “Sales-99 <= “Sales-retail”True

Conditions: Examples (Contd.) ► Assume a= 4; b= 3; c=“hello”; d=“bye” ► ExpressionTrue/False (a + b) < 2*a? (Len(c) - b) = (a/2)? c < “good” & d?

Conditions: Examples (Contd.) ► Assume a= 4; b= 3; c=“hello”; d=“bye” ► ExpressionTrue/False (a + b) < 2*aTrue (Len(c) - b) = (a/2)True c < “good” & dFalse

Conditions (Contd.) ► Condition is an expression involving relational operators; it is either True or False ► Relational operators: =; <>; ; = => See Table 5.1

Conditions (Contd.) ► Complex Conditions: Conditions joined by Logical Operators  cond1 And cond2  cond1 Or cond2  Not cond1

Conditions: Examples (Contd.) ► Assume n= 4; answ=“Y” ► ExpressionTrue/False (2<n)And(n<6) ? Not(n<6)? (answ=“Y”) Or (answ=“y”)?

Conditions: Examples (Contd.) ► Assume n= 4; answ=“Y” ► ExpressionTrue/False (2<n)And(n<6) True Not(n<6)False (answ=“Y”) Or (answ=“y”)True

Conditions (Contd.) ► Operator hierarchy: In decreasing order of priority:  Arithemetic  Relational  Logical ► Logical operator hierarchy: In decreasing order of priority:  Not  And  Or

Conditions (Contd.) => - Tie: Left most operator is first - Use parantheses

Decisions

Decision Structure: Flowchart Process Step (s) 2 Is Condition True Process Step (s) 1

IF BLOCKS IF condition Then action1Else action 2 action 2 End If

IF BLOCK (Contd.) ► Complete the program: Identifies and displays the larger value and its variable (assume unequal values) Sub Command1_Click Dim a As Single, b As Single, largerVal As Single Let a=4 Let b=5... Picture1. Print “Its value is:”;largerVal End Sub

IF BLOCK (Contd.) Sub Command1_Click Dim a As Single, b As Single, largerVal As Single Let a=4 Let b=5 If a>b Then Picture1.Print “a has the larger value” largerVal=aElse Picture1.Print “b has the larger value” largerVal=b End If Picture1. Print “Its value is:”;largerVal End Sub

IF BLOCK (Contd.) Result: b has the larger value Its value is: 5

IF BLOCK (Contd.) What the following program will do?

IF BLOCK (Contd.) Sub Command1_Click Dim a As Single, b As Single, largerVal As Single Let a=4 Let b=4 If (a>b) Or (a=b) Then Picture1.Print “a has the larger value” largerVal=aElse Picture1.Print “b has the larger value” largerVal=b End If Picture1. Print “Its value is:”;largerVal End Sub

IF BLOCK (Contd.) Result: a has the larger value Its value is: 4

IF BLOCK EXTENDED IF condition 1 Then action1 ElseIf condition 2 Then action 2 action 2 ElseIf condition 3 Then action 3 End If

IF BLOCK EXTENDED(Contd.) What the following program will do?

IF BLOCK EXTENDED(Contd.) Sub Command1_Click Dim a As Single, b As Single Let a=4 Let b=5 If (a>b) Then Picture1.Print “a has the larger value” ElseIf (a<b) Then Picture1.Print “b has the larger value” Else Picture1.Print “a and b have same value” End If End Sub

IF BLOCK EXTENDED (Contd.) Result: b has the larger value

Note: ► Read: Schneider (Section 5.1, 5.2) ► Read comments and do practice problems of these sections of these sections ► Attempt questions of Exercises