Visual C++ Programming: Concepts and Projects Chapter 11B: Pointers (Tutorial)

Visual C++ Programming: Concepts and Projects

Chapter 11B: Pointers (Tutorial)

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

2Programming with Visual C++

Problem Description


Problem Description (continued)


Design

• Interface sketch• Control table• Instance variables

– Data table– Drawing objects


Design (continued)


Design (continued)

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

data array text boxes needs starting and ending coordinates


Design (continued)


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)


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)


Design (continued)

• Algorithm for DrawLines()– Uses the following textbox properties

• Location.X• Location.Y• Width• Height


Design (continued)


Design (continued)

• Algorithm for DrawLines() (continued)– Draws lines connecting pointer array text boxes to

data array text boxes– Lines begin at the midpoint of the right side of

each pointer text box (ptrX, ptrY)


Design (continued)


Design (continued)

• Algorithm for DrawLines()(continued)– In this example, the pointer text boxes are

separated by 32 pixels vertically


Design (continued)


Design (continued)

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

appropriate data text box (arrX, arrY)– Variable startX stores the y coordinate of the first

data text box


Design (continued)


Design (continued)

• Algorithm for DrawLines() (continued)– 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)


Design (continued)

• Algorithm for DrawLines() (continued)– 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]) )


Design (continued)


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 text boxes– Displays the addresses of each element of the data

array • To the data text box labels• To the pointer array elements

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

boxes



• 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)



• The DisplayPointer() method– Displays pointer values on the interface



• 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 pointer array


Testing

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

generated and 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


On Your Own

• Descending order– Rewrite your bubble sort method

• Removing the swap() method– Place the instructions back in their proper place in

the bubble sort


Visual C++ Programming: Concepts and Projects Chapter 11B: Pointers (Tutorial)

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