int n = 7; int p = 11; int [] coll = new int[3] { 9, 17, 2 }; int [] group = new int[4] { -4, -3, -2, -8 };

Transcription

1 Array Assignments Page 1 A Simple Assignment Problem 2:27 PM Given some declarations: int n = 7; int p = 11; int [] coll = new int[3] { 9, 17, 2 }; int [] group = new int[4] { -4, -3, -2, -8 }; Execute these commands: group[0] = 2*group[1] - coll[1] ; n = coll[2] - group[0] ; group[2] = group[0] ; group[1] = group[2] - n ; Then enter the final values of each of the variables and each of the array elements.

2 Array Assignments Page 2 Array Assignments 2:24 PM These problems are pretty much algebra problems using arrays but the values of the variables and the elements of the arrays may be changing - sometimes several times. Three ideas can be used with these: 1. Layout a piece of paper to keep track of the values stored in the variables and in the arrays. Do this at the top of the page. 2. Divide that paper in half with a top half having the layout just discussed (wait to see a picture on the next slide). The bottom will the the assignment commands that are to be executed - but only written ONE AT A TIME. 3. Each assignment will be worked using substitution of values as is done in College Algebra.

3 Array Assignments Page 3 Layout Of The Work Consider the declaration part of the problem first given: int n = 7; int p = 11; int [] coll = new int[3] { 9, 17, 2 }; int [] group = new int[4] { -4, -3, -2, -8 }; Then layout the top half of your work sheet as follows: coll group Each variable and each array element will have a separate column in which to keep track of the series of values which may appear in that variable or array element.

4 Array Assignments Page 4 Initialize Layout Consider the declaration part of the problem first given: int n = 7; int p = 11; int [] coll = new int[3] { 9, 17, 2 }; int [] group = new int[4] { -4, -3, -2, -8 }; Use the initializations above to place values into the worksheet columns. coll group

5 Array Assignments Page 5 Begin First Command Below is the top of your worksheet: coll group Halfway down the workship begin the first command by copying it onto the worksheet (you can ignore the ;) : group[0] = 2 * group[1] - coll[1] Underneath that command, begin RE-writing the command with substitutions. For instance you can substitute a -3 in place of group[1] and a 17 in place of coll[1]. Those values were found in the columns at the top of the work sheet. Now your work should look like this: group[0] = 2 * group[1] - coll[1] = 2 * (-3) - 17

6 Array Assignments Page 6 Finish First Command Below is the top of your worksheet: coll group Halfway down the workship you should have this work: group[0] = 2 * group[1] - coll[1] = 2 * (-3) - 17 And you continue doing the algebra substitutions: group[0] = 2 * group[1] - coll[1] = 2 * (-3) - 17 = (-6) - 17 = And finally do the assignment: group[0] =

7 Array Assignments Page 7 Work on Second Command Below is the top of your worksheet: coll group Continuing the execution (not showing the first command) n = coll[2] - group[2] = 2 - (-2) = n = 4 Then do the assignment

8 Array Assignments Page 8 Work on Third Command Below is the top of your worksheet: coll group Continuing the execution (not showing the first two commands) group[2] = group[0] = group[2] = Note use of most recent value given to group[0] Then do the assignment

9 Array Assignments Page 9 Work on Fourth Command Below is the top of your worksheet: coll group Continuing the execution group[1] = group[2] - n = () - 4 = -27 Then do the assignment

10 Array Assignments Page 10 Enter Answers Below is the top of your worksheet: coll group Fill the FINAL answers into the appropriate equations: n = 4 p = 11 coll[0] = 9 coll[1] = 17 coll[2] = 2 group[0] = group[1] = -27 group[2] = group[3] = -8

11 Array Assignments Page 11 Medium Problem 3:16 PM Problems can involve algebra INSIDE of the subscript brackets [.]. int k = 0; int p = -3; int[] coll = new int[4] {9,1,2,5}; int[] row = new int[3] {11,-5,-1}; Worksheet Layout: coll row k p [0] [1] [2] [3] [0] [1] [2] Commands to execute: row[k+1] = coll[0]-k; row[p+5] = 2*row[p+4]-coll[0];

12 Array Assignments Page 12 Medium Command 1 3:16 PM coll row k p [0] [1] [2] [3] [0] [1] [2] Substitution in subscript of left hand side of assignment row[k+1] = coll[0] - k; = 9-0 row[k+1] = 9 row[0+1] = 9 row[1] = 9 assignment

13 Array Assignments Page 13 Medium Command 2 3:16 PM coll row k p [0] [1] [2] [3] [0] [1] [2] row[p+5] = 2 * row[p+4] - coll[0] = 2 * row[-3+4] - 9 = 2 * row[1] - 9 = 2 * 9-9 = 18-9 = 9 row[p+5] = 9 row[(-3)+5] = 9 substitute (-3) for p row[2] = 9 compute (-3)+5 Etc. etc. etc.

14 Array Assignments Page 14 Hard Problem 3:40 PM Declarations: int s = 5; int k = -5; int[] tab = new int[4] { -4, 11, 4, 6 }; int[] group = new int[4] { 12, 3, -9, 7 }; Worksheet layout: tab group s k [0] [1] [2] [3] [0] [1] [2] [3] Command to execute: tab[tab[s-2]-4] = 2*group[0]-group[group[k+7]+11];

15 Array Assignments Page 15 Hard Command 1 3:40 PM Worksheet layout: tab group s k [0] [1] [2] [3] [0] [1] [2] [3] Algebra: tab[tab[s-2]-4] = 2*group[0]-group[group[k+7]+11]; tab[tab[5-2]-4] = 2*12 -group[group[-5+7]+11]; tab[tab[ 3 ]-4] = 24 -group[group[ 2 ]+11]; tab[ 6-4] = 24 -group[ ]; tab[ 2 ] = 24 - group[ 2 ]; tab[2] = 24 - (-9) tab[2] = tab[2] = 33 Etc. etc. etc.