If a constant used in a program has a meaning, or it is possible that this constant may be changed in the future, the constant should be named. In general there should be no magic numbers or numbers that have a meaning but are not named, in a program.

Assume you are writing a program involving sales tax. The county tax rate is fixed at 4.75%. This rate will not change for the duration of the program, but in the future the tax rate may change, so this should be a named constant.

Acceptable Example

const float TAX_RATE = 0.0475;
...
 
tax = price * TAX_RATE;

Unacceptable Example:

tax = price * 0.0475;

At times the same constant may be given multiple names. Assume you are writing a program where the maximum number of items a person may purchase is 20. In addition, if the purchase price is over $20, the consumer will receive a discount. Each of these has a different meaning, so each should be declared as a named constant.

Acceptable Example:

const int MAX_ITEMS  = 20;
const int PRICE_BREAK = 20;
 
...
 
if (itemCount > MAX_ITEMS) {
 ...
}
 
if (price > PRICE_BREAK) {
    // the price was over $20, so give the customer a discount 
}

Unacceptable Example:

const int MAX_ITEMS = 20;
 
if (price > MAX_ITEMS) {
    // the price was over $20, so give the customer a discount
   ...
}

Note this is a very bad use. If the user decided to change MAX_ITEMS, a new bug would be introduced into the code.

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Unless otherwise instructed, a single prompt, the