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Multidimensional Arrays

Multidimensional Arrays. Array. Conceptual: List of objects indexed by a number What if we want more than one index??? Row / Col. Two-Dimensional Arrays. Two-Dimensional Array Logical matrix Declare: t ype identifier[ rows ][ cols ]; Rows then columns int scores[ 5 ][ 3 ];.

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Multidimensional Arrays

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  1. Multidimensional Arrays

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

  3. Two-Dimensional Arrays • Two-Dimensional Array • Logical matrix • Declare: type identifier[rows][cols]; • Rows then columns int scores[5][3];

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

  5. 2D Access • Access: scores[row][col] scores[4][0] = 10; cout << scores[2][1]; //outputs 93

  6. Storage • 2D arrays stored internally in row major order • First dimension is start address of row scores[1][??]

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

  8. Order: 0 0 0 1 0 2 1 0 1 1 1 2

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

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

  11. Sum all columns • Sum all columns: • Column is main loop, rows second:

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

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

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

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

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

  17. Passing Arrays • Must specify each dimension after first whenpassed as parameter

  18. Storage • 2D arrays stored internally in row major order • First dimension is start address of row scores[1][??]

  19. Passing Arrays • Compiles, but BAD

  20. Passing Arrays • Specify columns using global constant:

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

  22. Faking 2D • Can fake 2D with a 1D array • [row][col]  [colwidth*row][col] scores[1][2] scores[3*1 + 2]

  23. Multidimensional Arrays • Can have an arbitrary number of dimensions:

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