Section 2.2 discusses compilation units in detail. A compilation unit with no declarations is accepted with a compiler warning in all modes except for the strict ANSI standard mode. 1.1 Character Set A character set defines the valid characters that can be used in source programs or interpreted when a program is running. The source character set is the set of characters available for the source text. The execution character set is the set of characters available when executing a program.
C treats each character as a different integer value.
However, in some extended character sets, so many characters exist that some characters' representation requires more than 8 bits. Section 1.8.3.1 discusses wide characters further. Section 1.8.3.3 and Section 1.8.3.4 describe these escape sequences. The null character is a byte or wide character with all bits set to 0. It is used to mark the end of a character string.