Multidimensional Arrays

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# Multidimensional Arrays - PowerPoint PPT Presentation

Multidimensional Arrays. Chapter 13. The plural of mon goose starts with a &quot;p&quot;. 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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## PowerPoint Slideshow about 'Multidimensional Arrays' - Philip

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### Multidimensional Arrays

Chapter 13

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
• 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

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
• 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 Arrays
• What does the routine below do with the array? What should we name the function?

total_a_row

0

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 Arrays
• This function initializes an array.
• Fill in the blanks with the correct identifiers

3

col

table

value

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
• 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
• 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
• 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 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 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
• Initialize all components of an array
• 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 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 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