Multidimensional Arrays

1
Multidimensional Arrays

• Chapter 13

2
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
3
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 components position in each
  dimension

0 1 2 3 4
0 1 2 3
Which cell isLocation (2,3) ?
4
Declaring Two Dimensional Arrays

• Syntax data_type array_name row_dimcol_dim
  
• Example
• First element isint_table00
• Last element isint_table43

int int_table 54
5
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 54int row, col
6
Processing Two-D Arrays

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

total_a_row
0
7
Processing Two-D Arrays

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

total_column
0
8
Processing Two-D Arrays

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

3
col
table
value
9
Printing a Table

• 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
10
Passing Arrays as Parameters

• Recall declaration for 1-D array
• we didnt 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)
11
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)
12
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 12rent_pmts renters
6
0 1 10 11
0 1 5
13
Multidimensional Arrays

• C arrays not limited to two dimensions
• limitation is amount of memory

const int NUM_BLDGS 10const int APTS_PER_BLDG
12float apt_pmts NUM_BLDGS6APTS_PER_BLDG

14
Multidimensional Arrays

• C arrays not limited to two dimensions
• limitation is amount of memory

const int NUM_BLDGS 10const int APTS_PER_BLDG
12float apt_pmts NUM_BLDGS6APTS_PER_BLDG

This gives a 3-D array with 720 itemsapt_pmt
bldgtennantapt
15
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
• dont reverse row and column references

16
Testing and Debugging

• Use meaningful identifiers for the array name and
  indeces
• Double check upper and lower bounds on indeces
• dont walk off the edge of the array
• When declaring multidimensional array as a formal
  parameter
• must state sizes of all but first dimension

17
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