1. ME 142 Engineering Computation I Loops

2. Key Concepts Looping Basics For… Next Statement Do… Loop Statement For Each… Next Statement

3. Looping Basics

4.  The term loop or looping refers to repeating a block of code multiple times.  Must be able to end loop – otherwise infinite loop!! Execute pre-determined number of times Execute until a condition is satisfied

5. For...Next Statement

6. For… Next Statement The For… Next statement is used to repeatedly execute a block of statements a specified number of times. For counter = start to end [Step stepsize] [statements] Next [counter]

7. For… Next Example For I = 1 to 5 Cells(I,1) = I Next I

8. For… Next Example For I = 1 to 5 ActiveCell.Value = I ActiveCell.Offset(1,0).Select Next I

9. For… Next Example Sub demo() ‘Computes average of cells A1:A5 Total = 0 For i = 1 To 5 Total = Total + Cells(i, 1) Next I Average = Total / 5 MsgBox "Average = " & Average End Sub

10. Example Problem  Create a factorial function using For Next loops. Pass the function the number whose factorial is to be computed. After computing the factorial, the results should be displayed in the cell from which the function is called.  Use the factorial function you created to compute the factorials for the integers 1 through 10.

11. Example Problem Soln Function factorial(n) 'computes the factorial of a number Total = 1 For i = 1 To n Total = Total * i Next i factorial = Total End Function

12. Do...Loop Statement

13. Do… Loop Statement  The Do… Loop statement is used to repeatedly execute a block of statements until a specified condition is met. Conditions are tested using While and Until at either the beginning or end of the loop.

14. Do… Loop Statement Do [While condition] [statements] Loop Do [statements] Loop [While condition] Do [Until condition] [statements] Loop Do [statements] Loop [Until condition] Do [statements] Loop

15. Do… Loop Example x = 1 Do Cells(x,1) = x x = x + 1 Loop Until x = 5 x = 1 Do Until x =5 Cells(x,1) = x x = x + 1 Loop

16. Do… Loop Example x = 10 Do Cells(x,1) = x x = x + 1 Loop Until x = 5 Use Ctrl+Break or Esc to stop execution of infinite loop

17. Do… Loop Example x = 10 Do Cells(x,1) = x x = x + 1 Loop Until x> = 5 x = 10 Do Until x >=5 Cells(x,1) = x x = x + 1 Loop

18. Example Problem  Create a factorial function using Do loops. Pass the function the number whose factorial is to be computed. After computing the factorial, the results should be displayed in the cell from which the function is called.  Use the factorial function you created to compute the factorials for the integers 1 through 10.

19. Example Problem Soln Function factorial(n) 'computes the factorial of a number Total = 1 I = 1 Do While I <= n Total = Total * I I = I + 1 Loop factorial = Total End Function

20. For Each...Next Statement

21. For Each… Next Statement The For Each…Next statement is used to loop through each object in a collection of objects. An example of this would be to loop through each of the cells in a range of cells. For Each element In collection [statements] Next [element]

22. For Each… Next Example Function ForEachDemo(MyRange) Total = 0 For Each Cell In MyRange Total = Total + Cell.Value Next Cell ForEachDemo = Total End Function

23. For Each… Next Example Sub FillDemo() ‘Fill a selection with random numbers For Each cell In Selection cell.Value = Rnd Next cell End Sub

24. Review Questions

25. Review Question What is the value of Count after the loop has finished executing: Count=0 For I = 1 to 5 Count = Count + I Next I A.0 B.5 C.10 D.15 E.None of the above

26. Review Question What is the value of Count after the loop has finished executing: x=1 Count=0 Do Count = Count + x x = x + 1 Loop Until x = 5 A.0 B.5 C.10 D.15 E.None of the above

27. Homework Help ‘n Hints