Demonstrating Pointers in C

One aspect of programming which many students find difficult is pointers. Put simply, pointers are variables which store addresses. Below, you will find an applet which will introduce a few of the fundamentals of pointers, as well as a few warnings of pitfalls to avoid when using pointers. The applet includes sample code in C, sample output, explanations of the lines of code, and a simulation of what is happening in memory.

Accessing Different Concepts

To change between pointer concepts illustrated by the applet, click on the pull-down menu which begins with “Basic Pointers” and select a new concept from the list. New program code will appear in the program code window.

Moving through the Program Code

There are three ways to move through the program code:

• Click on the “Forward” and “Back” to move from line to line.
• Use the up and down arrow keys on the keyboard to move from line to line.
• Click on an individual line of the code with the mouse. Clicking on any line will invoke the lines before it, as if they had already been run through.

Changing Notation

To change between decimal, binary, hexadecimal, and ASCII notation as displayed in the simulation of memory on the right side of the applet, click on the pull-down menu which begins with “Decimal” and select a new notation from the list. Upon changing notation, the line of code active in the code window will return to the first line of the code, and the representation of values stored in memory and memory addresses changes to the correct notation type.

Understanding the Interface

• Program Controls appear in the upper left corner of the applet.
• Program Code Area appears in the middle of the left side of the applet.
• Program Output Area appears in black with white type beneath the Program Code Area on the left side.
• Explanation Area appears across the bottom of the applet in blue with yellow type and describes what is happening in memory as the program executes the highlighted line of code.
• Memory Representation Area appears on the right side of the applet including a list of address locations, a list of variables located in the address locations, and the values stored in specific locations.