Visual C++ Programming: Concepts and Projects

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 Programming with Visual C++

Problem Description Programming with Visual C++

Problem Description (continued) Programming with Visual C++

Design • Interface sketch • Control table • Instance variables • Data table • Drawing objects Programming with Visual C++

Design (continued) Programming with Visual C++

Design (continued) • Variables for DrawLines() • Each line drawn from the pointer array to the data array text boxes needs starting and ending coordinates Programming with Visual C++

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 Programming with Visual C++

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 Programming with Visual C++

Design (continued) • Algorithm for DrawLines() • Uses the following textbox properties • Location.X • Location.Y • Width • Height Programming with Visual C++

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) Programming with Visual C++

Design (continued) • Algorithm for DrawLines()(continued) • In this example, the pointer text boxes are separated by 32 pixels vertically Programming with Visual C++

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 Programming with Visual C++

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) Programming with Visual C++

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]) ) Programming with Visual C++

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 Programming with Visual C++

Development (continued) Programming with Visual C++

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 Programming with Visual C++

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) Programming with Visual C++

Development (continued) • The DisplayPointer() method • Displays pointer values on the interface Programming with Visual C++

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 pointer array Programming with Visual C++

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 Programming with Visual C++

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 Programming with Visual C++

Visual C++ Programming: Concepts and Projects