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Nested conditionals are by their very nature complicated. So it is usually better to avoid them whenever possible. An exception to this rule is a special form of nested conditional where all except possibly the last else is immediately followed by another i f. This is a popular logical structure because it delineates in a simple way a sequence of disjoint alternatives. To clarify the logic, programmers usually line up the e 1 se i f phrases, as shown in the next example. 14 This program converts a test score into its equivalent letter grade: main0 .

Then, since 33 is not greater than 77, max is unchanged. Finally, since 55 is also not greater than 77, max is again unchanged, and so the value 77 is printed. 5 COMPOUND STATEMENTS A compound statement is a sequence of statements that is treated as a single statement. C++ identifies a compound statement by enclosing its sequence of statements in curly braces. The next example contains the following compound statement: int temp = x; x = y; Y = temp; The braces that enclose the three statements form a block.

The last line in the program uses the scope resolution operator : : to access the global x that is otherwise hidden in main ( ) . 13 ENUMERATION TYPES In addition to the predefined types such as int and char, C++ allows you to define your own special data types. This can be done in several ways, the most powerful of which use classes as described in Chapters 8-14. We consider here a much simpler kind of user-defined type. An enumeration type is an integral type that is defined by the user with the syntax enum typename { enumeratorlist }; Here enum is a C++ keyword, typename stands for an identifier that names the type being defined, and enumera tori is t stands for a list of identifiers that define integer constants.