Differences

This shows you the differences between two versions of the page.

--- guides:programstyle:constants [2020/07/24 11:49] – wikiadmin
+++ guides:programstyle:constants [2022/08/02 11:59] (current) – external edit 127.0.0.1
@@ Line 20: / Line 20: @@
 </code>
-Unless otherwise instructed, a single prompt, the
+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:
+<code c++>
+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
+}
+</code>
+Unacceptable Example:
+<code c++>
+const int MAX_ITEMS = 20;
+if (price > MAX_ITEMS) {
+    // the price was over $20, so give the customer a discount
+   ...
+}
+</code>
+Note this is a very bad use.  If the user decided to change MAX_ITEMS, a new bug would be introduced into the code.
+In the last example, a programmer might be tempted to employ the following definition
+<code c++>
+const int TWENTY = 20;
+</code>
+This is unacceptable for multiple reasons.
+  * TWENTY is no more informative than 20.
+  * If the value of the constant changed, the programmer might be tempted to produce the following totally unacceptable code
+    * <code c++>
+const int TWENTY = 35;
+</code>
+Unless otherwise instructed, single use constants are usually not named unless they provide clarity to the program.  Examples include a prompt used one time or an arbitrary field width.
+The following is probably not necessairy
+<code c++>
+const int FIRST_FIELD_WITDTH = 20;
+const string FIRST_PROMPT = "Enter your Age";
+...
+cout << setw(FIRST_FIELD_WIDTH) << FIRST_PROMPT << endl;
+</code>