Debugging by Thinking

Preface

Why I Wrote This Book

When I first learned to program, I found the process of testing and debug-

ging very frustrating. I can remember slamming my fist down on the hard

metal shell of the Selectric typewriters we used to interact with the time-

sharing system at the amazing speed of 15 characters per second. The bugs

didn't disappear any more quickly for the beating. None of my professors

taught me anything about testing and debugging that I can remember.

During the nearly 30 years that I have worked in software development,

many aspects of the profession have changed. Languages have become pop-

ular and gone out of favor. Better development methodologies have been

introduced, only to be replaced by yet more sophisticated methodologies.

Microprocessors have become ubiquitous, and software has become the

driving force behind many new products. The laptop computer that I wrote

this book on has a faster processor, more memory, and more disk space than

the multimillion dollar IBM

TM

mainframe on which I learned to program.

Some things have not changed, however. Software products still contain

far too many bugs. Software developers still spend far too much time find-

ing and fixing those bugs. People who are learning to program spend far too

much time struggling to learn by trial and error.

I wrote this book because I wanted to introduce a systematic approach to

debugging to a wide audience. If you learn something from this book that

enables you to find and fix bugs more quickly, then I will have succeeded.

Who Should Read This Book

This book was written with both students and professional programmers in

mind. Any student who has completed a course in computer programming

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