460 Appendix A C Language Summaryexpressionis evaluated and compared against the constant expression values
constant_1,constant_2,...,constant_n. If the value of expressionmatches one of these
case values, the program statements that immediately follow are executed. If no case
value matches the value of expression, the default case, if included, is executed. If the
default case is not included, no statements contained in the switch are executed.
The result of the evaluation of expressionmust be of integral type and no two cases
can have the same value. Omitting the breakstatement from a particular case causes
execution to continue into the next case.8.11 The whileStatement
The general format for declaring the whilestatement is as follows:
while ( expression)
programStatement
programStatementis executed as long as the value of expressionis nonzero. Note that,
because expressionis evaluated each time beforethe execution of programStatement,
programStatementmight never be executed.9.0 The Preprocessor
The preprocessor analyzes the source file before the compiler properly sees the code.The
preprocessor does the following:- Replaces trigraph sequences (See Section 9.1) by their equivalents
- Joins any lines that end with a backslash character () together into a single line
- Divides the program into a stream of tokens
- Removes comments, replacing them with a single space
- Processes preprocessor directives (see Section 9.2) and expands macros
9.1 Trigraph Sequences
To handle non-ASCII character sets, the three-character sequences (called trigraphs) listed
in Table A.7 are recognized and treated specially wherever they occur inside a program
(as well as inside character strings):Ta ble A.7 Tr igraph Sequences
Tr igraph Meaning
??= #
??( [
??) ]
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