Introduction to Computing

1. Introduction to Computing Dr. Nadeem A Khan

2. Lecture 19

3. Lecture 20 in Lab !

4. Functions

5. 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

6. 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

7. 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

8. Functions (Contd.) • Result: 100 0 45

9. Functions (Contd.) • 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

10. 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

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

12. 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

13. Modular Design • Top-Down Design • Structured Programming • Sequences • Decisions • Loops

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

15. Conditions

16. Conditions: Examples • Expression True/False 2 < 5 ? -5 > -2.5 ? 1 < 1 ? 1 = 1 ? 3.5 <= 3.5 ? -9 >= -35 ? -2 <> -3 ?

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

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

19. Conditions: Examples (Contd.) • For strings use the ANSI (or ASCI) table Characters ANSI(ASCI) Value Digits (0-9) 48-57 Upper Case (A-Z) 65-90 Lower Case (a-z) 97-122 • Compare two strings character by character

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

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

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

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

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

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

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

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

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

29. Decisions

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

31. IF BLOCKS IF condition Then action1 Else action 2 End If

32. 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

33. 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=a Else Picture1.Print “b has the larger value” largerVal=b End If Picture1. Print “Its value is:”;largerVal End Sub

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

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

36. 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=a Else Picture1.Print “b has the larger value” largerVal=b End If Picture1. Print “Its value is:”;largerVal End Sub

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

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

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

40. 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

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

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