1. ME 142 Engineering Computation I More Loops & Arrays

2. Key Concepts Nesting Loops Dynamic Arrays Multi-Dimensional Arrays

3. Nesting Loops

4. Nesting  What is Nesting?  How do you Nest loops?

5. Nesting Example Counter = 1 For I = 1 to 5 For J = 1 to 4 Cells(I,J) = Counter Counter = Counter + 1 Next J Next I

6. Dynamic Arrays

7. Dynamic Array  Created without a preset number of elements  When using dynamic arrays, number of elements is typically determined when code is run  Use ReDim command to establish number of elements  Dynamic arrays can be reused

8. Dynamic Array Syntax Dim ArrayName() … ReDim ArrayName(NumElements)

9. Dynamic Array Example Sub ReDimDemo() Dim A() Num = Val(InputBox("Enter number")) ReDim A(1 To Num) For i = 1 To Num A(i) = InputBox("Enter name") Next I For i = 1 To Num Cells(1, i) = A(i) Next I End Sub

10. Multi-Dimensional Arrays

11.  Can be used to store a 2-D or 3-D grid of data as opposed to just a row or column  Array Comparisons: Spreadsheet row- 1-dimensional array Spreadsheet column- 1-dimensional array Worksheet- 2-dimensional array Workbook- 3-dimensional array

12. Example Problem  Use a two dimensional array to create table of temperatures and their conversions. User will be prompted for number of Temperatures User will enter temperatures in degrees F Program will convert temperatures to C, K, & R Program will create table all 4 temperatures

13. Sub MultArr() 'Temperature conversion example 'Get # of Temps Dim Temp() N = InputBox("Enter number of temperatures to convert") ReDim Temp(1 To N, 1 To 4) 'Read in F Temps For i = 1 To N Temp(i, 1) = InputBox("Enter Temp #" & i) 'read F temp. Next i 'Continued next slide…

14. 'Convert Temps For i = 1 To N Temp(i, 2) = (Temp(i, 1) - 32) * 5 / 9 'convert to C Temp(i, 3) = Temp(i, 2) + 273 'convert to K Temp(i, 4) = Temp(i, 1) + 460 'convert to R Next i 'Write Table For i = 1 To N For j = 1 To 4 Cells(i + 1, j) = Temp(i, j) 'write temp. Next j Next i End Sub

15. Example Problem  Use nested For Next loops to create a grid of random 2 digit numbers. Read directly from spreadsheet cells the number of rows and columns in the grid to be created.

16. Sub CreateGrid() 'Creates a grid of random numbers 'read rows and columns from spreadsheet NRow = Cells(2, 1) NCol = Cells(2, 2) Randomize For i = 1 To NRow For j = 1 To NCol Cells(i + 3, j) = Round(Rnd, 2) Next j Next i End Sub

17. Review Questions

18. Review Question Which of the following are valid examples of nesting loops: A.Example #1 B.Example #2 C.Example #3 D.Both Examples #1 &#2 E.Both Examples #1 & #3 For I = 1 to N For J = 1 to M … Next J Next I For I = 1 to N For J = 1 to M … Next I Next J For I = 1 to N … Next I For J = 1 to M … Next J Example #1Example #2Example #3

19. Review Question Multi-Dimensional Arrays How many elements may be stored in the following array: Dim MyArray(1 to 100, 1 to 100, 1 to 100) A.100 B.300 C.1000 D.10,000 E.1,000,000

20. Homework Help ‘n Hints