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Understanding Multidimensional Arrays in Programming

Learn about multidimensional arrays, from declaring and initializing to accessing elements, storage, traversals, and sums of rows and columns in the array. Explore concepts and practical uses.

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Understanding Multidimensional Arrays in Programming

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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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