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Introduction to Computing

Introduction to Computing. Dr. Nadeem A Khan. Lecture 23. Subprograms /Subroutines revisited. Subprograms. General Format Sub SubprogrammeName ( list of parameters ) statements End Sub. Subprograms (Contd.). Examples: Sub ExplainPurpose ( )

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Introduction to Computing

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  1. Introduction to Computing Dr. Nadeem A Khan

  2. Lecture 23

  3. Subprograms /Subroutinesrevisited

  4. Subprograms • General Format Sub SubprogrammeName (list of parameters) statements End Sub

  5. Subprograms (Contd.) • Examples: Sub ExplainPurpose () Rem Explain the task performed by the program Picture1.Print “This program displays sentences” Picture1.Print “identifying pair of numbers and their sums.” End Sub Sub Add ( num1 As Single, num2 As Single) Rem Display numbers and their sum • Picture1.Print “Sum of”; num1; “and”; num2; “is”; num1+num2 End Sub

  6. Subprograms (Contd.) • Using subprograms in a Program Sub Command1_Click( ) Rem Display the sum of several pairs of numbers Picture1.Cls Call ExplainPurpose Picture1.Print Call Add(2, 3) Call Add(4, 6) Call Add(7, 8) End Sub

  7. Subprograms (Contd.) • Local variables • Form-level variables

  8. Subprograms: Passing Variables • Example 1: Subroutine Sub Triple( num As Single) Rem Triples a number Picture1.Print num; Let num = num*3 Picture1.Print num; End Sub

  9. Subprograms: Passing Variables • Example 1: Program Sub Command1_Click( ) Dim amt As Single Picture1.Cls Let amt=2 Picture1.Print amt; Triple(amt) Picture1.Print amt End Sub

  10. Subprograms: Passing Variables • Example 1: Result 2 2 6 6 => Variable was passed by reference in Example 1

  11. Functions

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

  13. Functions • Example: Function FtoC (t As Single) As Single FtoC = (5/9)*(t-32) End Function

  14. 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

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

  16. Functions • Another Example: 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 Write a program which input the full name and output the first name to the user using this function!

  17. 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

  18. 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

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

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