For more information on how to write efficient programs, refer to the following books:

The Elements of Programming Style, Second Edition
Kernighan & Plauger
McGraw-Hill
ISBN 0-07-034207-5

Writing Efficient Programs
Jon Louis Bentley
Prentice-Hall Software Series
ISBN 0-13-970244-X

Algorithms in C
Robert Sedgewick
Addison Wesley
ISBN 0-201-51425-7

Data Structures, Algorithms & Software Principles in C
Thomas A. Standish
Addison Wesley
ISBN 0-201-59118-9