Logical Level

• consists of finite, fixed-size collection of ordered hmogenous (same type) elements
• component selection = direct access (do not have to first access preceeding elements).

Application Level

Storage for lists of Things.

e.g. Name List, Customer List, Products list

Implementation Level

type Array[num];

• indexed from 0 to num-1
• Number of elements num
• Base Addres = ? (run time variation)
• Size of Element = sizeof type in bytes

float values[5];

Q: Arrays in C++ are always passed by reference (e.g. type function(int array[],...) )
How can we prevent change to an array?

A: Declare array as a const parameter

type function ( const int array[], .....)

now can only access elements or array but not alter their contents.

N-D arrays

• declaraction     int A[10][6];
• parameter in function     type function(int A[][6],....)

The size of all dimensions except the first must be included in the function heading and prototype.

• In memory, C++ stores arrays in row order. The first row is followed by the second row, etc.

Arrays cannot be assigned one to another, and cannot be the return type of a function.

Using typedef with arrays

helps eliminate the chances of size mismatches between formal and actual parameters

typedef int StateHighsType [ NUM_STATES ] [ NUM_MONTHS ] ; typedef int StateAveragesType [ NUM_STATES ] ; void findAverages( const StateHighsType stateHighs , StateAveragesType stateAverages ) { . . . }

 

const int NUM_DEPTS = 5; // mens, womens, childrens, electronics, linens const int NUM_MONTHS = 12 ; const int NUM_STORES = 3 ; // White Marsh, Owings Mills, Towson typedef long MonthlySalesType [NUM_DEPTS] [NUM_MONTHS] [NUM_STORES]; MonthlySalesType monthlySales;

 

 

 

Deleting an Array

To delete an array, we need to tell the compiler we are deleting an array, and not just an element. The syntax is:

delete [] arrayName;

Deleting 2d arrays takes a little more work. Since a 2d array is an array of arrays, we must first delete all the elements in each of the arrays, and then we can delete the array that contains them.

Assuming we had created a 2d array called 2dArray, we could delete it as follows: for(int i=0; i < (number of arrays); i++)
         delete [] 2dArray[i];

delete [] 2dArray;