C Primer Plus®, Third Edition

Data Variables and Constants

A computer, under the guidance of a program, can do many things. It can add numbers, sort names, command the obedience of a speaker or video screen, calculate cometary orbits, prepare a mailing list, dial phone numbers, draw stick figures, draw conclusions, or anything else your imagination can create. To do these tasks, the program needs to work with data, the numbers and characters that bear the information you use. Some data are preset before a program is used and keep their values unchanged throughout the life of the program. These are constants. Other data may change or be assigned values as the program runs; these are variables. In the sample program, weight is a variable and 14.5833 is a constant. What about ...