CHAPTER 11B POINTERS

Tutorial: Sorting with a Pointer Array

Tutorial: Sorting with a Pointer Array Problem Description

Create an array of integers and display its values and the address of each element

Create an array of pointers to integers Assign the address of each element in the

integer array to the corresponding elements of the pointer array

Sort the data by swapping pointers Display the sorted data by using a for loop

to access each element of the pointer array

Design

Interface sketch Control table Instance variables

Data table Drawing objects

Design (continued)

Variables for DrawLines() Each line drawn from the pointer array

to the data array textboxes need starting and ending coordinates

Design (continued)

Event handlers btnData_Click()

Generates random numbers in the data array Captures data array element addresses and

assigns to the pointer array Displays data and pointers Draws lines connecting them

Design (continued)

Event handlers btnSort_Click()

Sort the data by swapping pointers Draw lines from each pointer to the appropriate

data item Display the sorted data in a MessageBox

Design (continued)

Algorithm for DrawLines() Uses the following textbox properties

Location.X Location.Y Width Height

Design (continued)

Algorithm for DrawLines() Draws lines connecting pointer array

textboxes to data array textboxes Lines begin at the midpoint of the right side

of each pointer textbox (ptrX, ptrY)

Design (continued)

Algorithm for DrawLines() In this example, the pointer textboxes are

separated by 32 pixels vertically

Design (continued)

Algorithm for DrawLines() Lines end at the midpoint of the left side of

the appropriate data textbox (arrX, arrY) Variable startX stores the y coordinate of

the first data textbox

Design (continued)

Algorithm for DrawLines() The location of arrY is calculated by

Determining how many elements away from the first element you must go

Multiplying the number of elements by 32 (the number of pixels separating each element)

Design (continued)

Algorithm for DrawLines() To determine how many elements away

from the first element you must go, subtract the pointer array value from the address of the first data element ( &(arr[0]) )

Development

The Interface Based on Figure 11-32

Coding Instance variable declarations and

Form1_Load() The btnData_Click() event handler The btnSort_Click() event handler The drawLines() method

Development (continued)

The btnData_Click() event handler Assigns random numbers to each array element Displays the data values in arr to the data

textboxes Displays the addresses of each element of the

data array To the data textbox labels To the pointer array elements

Displays the pointer array values Draws the lines connecting pointer and data

textboxes

Development (continued)

The btnSort_Click() event handler Sorts the pointer array according to the

values in the data array Displays the pointers Creates output string Draws the connecting lines (once before

and once after the MessageBox is displayed)

Development (continued)

The DisplayPointer() method Displays pointer values on the interface

Development (continued)

The drawLines() method Calculates ptrX, ptrY Calculates the corresponding arrX and arrY Draws lines between (ptrX, ptrY) on the

pointer array and (arrX, arrY) on the data array for each element of the poniter array

Testing

Run your program several times btnSort should be initially disabled When btnData is clicked random numbers

are generated, displayed, and the memory cell addresses of the data array are displayed

When btnSort is clicked the pointer array elements are swapped until they point to the data array elements in sorted order