Multidimensional Arrays

Array Conceptual: What if we want more than one index??? List of objects indexed by a number What if we want more than one index??? Row / Col

Two-Dimensional Arrays Logical matrix Declare: type identifier[rows][cols]; Rows then columns int scores[5][3]; 1 2 76 82 83 84 94 88 93 3 91 98 4

Initialization Initialize as list of lists: Zero out entire array: int nums[3][4] =  {{19,22,31,42},                   {50,61,32,83},                    {93,47,15,66}}; Zero out entire array: int nums[3][4] =  {{0}};

2D Access Access: scores[row][col] scores[4][0] = 10; cout << scores[2][1]; //outputs 93 1 2 76 82 83 84 94 88 93 3 91 98 4 10

Storage 2D arrays stored internally in row major order scores[1][??] First dimension is start address of row scores[1][??] 1 2 76 82 83 84 94 88 93 1 2 3 4 5 6 7 8 76 82 83 84 94 88 93

Traversals Traverse with nested loops Row index/col index Loop order matters

Loop Samples i, j aren't great, but get used to them Use constants for loop conditions

Single Dimension Traversals Traversing one row or column requires one loop, one hardcoded index

Sum all columns Sum all columns: Column is main loop, rows second:

Sum Rows And Columns Use arrays of row totals / col totals to build all sums 1 4 2 5 9 7 1 2 1

Sum Rows And Columns Use arrays of row totals / col totals to build all sums 1 4 2 5 9 7 1 2 4 1 4

Sum Rows And Columns Use arrays of row totals / col totals to build all sums 1 4 2 5 9 7 1 2 6 1 4 2

Sum Rows And Columns Use arrays of row totals / col totals to build all sums 1 4 2 5 9 7 1 2 6 5 1 9 2

Sum Rows And Columns Use arrays of row totals / col totals to build all sums

Passing Arrays Must specify each dimension after first when passed as parameter

Storage 2D arrays stored internally in row major order scores[1][??] First dimension is start address of row scores[1][??] 1 2 76 82 83 84 94 88 93 1 2 3 4 5 6 7 8 76 82 83 84 94 88 93

Passing Arrays Compiles, but BAD

Passing Arrays Specify columns using global constant:

Passing Arrays Same using defined global constants: Don't need to pass number rows Still need to specify array second dimension

Faking 2D Can fake 2D with a 1D array scores[1][2] scores[3*1 + 2] [row][col]  [colwidth*row][col] 1 2 76 82 83 84 94 88 93 scores[1][2] scores[3*1 + 2] 3*0 + 0 3*0 + 1 3*0 + 2 3*1 + 0 3*1 + 1 3*1 + 2 3*2 + 0 3*2 + 1 3*2 + 2 1 2 3 4 5 6 7 8 76 82 83 84 94 88 93

Multidimensional Arrays Can have an arbitrary number of dimensions: