Programming in C

426 Appendix A C Language Summary

must be a letter, underscore, or a universal character name.The first 31 characters of an

identifier are guaranteed to be significant in an external name, and the first 63 characters

are guaranteed to be significant for an internal identifier or macro name.

1.2.1 Universal Character Names

A universal character name is formed by the characters \ufollowed by four hexadecimal

numbers or the characters \U followed by eight hexadecimal numbers. If the first char-

acter of an identifier is specified by a universal character, its value cannot be that of a

digit character. Universal characters, when used in identifier names can also not specify a

character whose value is less than A0 16 (other than 24 16 ,40 16 , or 60 16 ) or a character in

the range D800 16 through DFFF 16 ,inclusive.

Universal character names can be used in identifier names, character constants, and

character strings.

1.2.2 Keywords

The identifiers listed in Table A.2 are keywords that have a special meaning to the C

compiler.

Ta ble A.2 Keywords

_Bool default if sizeof while

_Complex do inline static

_Imaginary double int struct

auto else long switch

break enum register typedef

case extern restrict union

char float return unsigned

const for short void

continue goto signed volatile

2.0 Comments

You can insert comments into a program in two ways. A comment can begin with the

two characters //.Any characters that follow on the line are ignored by the compiler.

A comment can also begin with the two characters /*and end when the characters

*/are encountered. Any characters can be included inside the comment, which can

extend over multiple lines of the program. A comment can be used anywhere in the pro-

gram where a blank space is allowed. Comments, however, cannot be nested, which

means that the first */characters encountered end the comment, no matter how many

/*characters you use.

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