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Multidimensional Arrays. Chapter 13. The plural of mon goose starts with a "p". Initializing a multidimensional array. 0 1 2 3 4. Processing by row. 0 1 2 3. Printing the contents of an array. Processing by column. Two dimensional Arrays.

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the plural of mon goose starts with a p
The plural of mongoose starts with a "p"

Initializing a multidimensionalarray

0 1 2 3 4

Processingby row

0

1

2

3

Printing thecontents ofan array

Processingby column

two dimensional arrays
Two dimensional Arrays
  • A collection of components
    • all of the same type
    • structured in TWO dimensions
    • each component accessed by a PAIR of indices representing the component’s position in each dimension

0 1 2 3 4

0

1

2

3

Which cell isLocation (2,3) ?

declaring two dimensional arrays
Declaring Two Dimensional Arrays

0 1 2 3 4

0

1

2

3

  • Syntax: data_type array_name [row_dim][col_dim];
  • Example:
  • First element isint_table[0][0]
  • Last element isint_table[4][3]

int int_table [5][4];

processing two d arrays
Processing Two-D Arrays
  • Arrays processed in some pattern
    • random
    • along rows
    • along columns
    • whole array
  • We will use the declaration shown below:

int int_table [5][4];int row, col;

processing two d arrays6
Processing Two-D Arrays
  • What does the routine below do with the array? What should we name the function?

total_a_row

0

processing two d arrays7
Processing Two-D Arrays
  • What does this routine below do with the array? What should we name the function?

total_column

0

processing two d arrays8
Processing Two-D Arrays
  • This function initializes an array.
  • Fill in the blanks with the correct identifiers

3

col

table

value

printing a table
Printing a Table

row

row

row

col

col

col

  • We must process each row, item by item
  • Which will be the inner loop?Which will be the outer loop?
  • The LCV of the inner loop must be the one which changes the most often

What goeshere?

endl

passing arrays as parameters
Passing Arrays as Parameters
  • Recall declaration for 1-D array
  • we didn’t specify the size in the brackets
    • we sent the size as a separate parameter
  • Recall name of the array is a pointer constant
    • tells where the array starts in memory
    • this is what is passed to the function

void whatever ( float num_list [ ], int size);

passing 2 d arrays as parameters
Passing 2-D Arrays as Parameters
  • For a 2-D array, declare
  • We are sending the starting address
    • also how many elements it takes to jump us to the next row
    • that is -- the number of columns
  • Note that this could be for an array for ANY number of rows, but exactly 4 columns
  • As with 1-D, we also send another parameter for the function as a limiting value

void whatever ( float num_table [ ][4], int num_rows);

alternate 2 d array definition
Alternate 2-D Array Definition
  • Think of the 2-D array as an array of arrays
  • Example
  • Each element of renters is an array of rent_pmts

typedef float rent_pmts [12];rent_pmts renters [6];

0 1 … 10 11

0

1

5

multidimensional arrays13
Multidimensional Arrays
  • C++ arrays not limited to two dimensions
    • limitation is amount of memory

const int NUM_BLDGS = 10;const int APTS_PER_BLDG = 12;float apt_pmts [NUM_BLDGS][6][APTS_PER_BLDG];

multidimensional arrays14
Multidimensional Arrays
  • C++ arrays not limited to two dimensions
    • limitation is amount of memory

const int NUM_BLDGS = 10;const int APTS_PER_BLDG = 12;float apt_pmts [NUM_BLDGS][6][APTS_PER_BLDG];

This gives a 3-D array with 720 itemsapt_pmt [bldg][tennant][apt]

testing and debugging
Testing and Debugging
  • Initialize all components of an array
    • no guarantee of what is there to start with
  • Use the same number of indeces as the declaration of array
  • Make sure indeces are in order
    • don’t reverse row and column references
testing and debugging16
Testing and Debugging
  • Use meaningful identifiers for the array name and indeces
  • Double check upper and lower bounds on indeces
    • don’t walk off the edge of the array
  • When declaring multidimensional array as a formal parameter
    • must state sizes of all but first dimension
testing and debugging17
Testing and Debugging
  • When calling function with array as parameter
    • sizes of multi-dim actual parameter must match exactly sizes of formal
  • Use typedef statement to define multi-dimensional array type
    • use this for actual and formal parameter declaration
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