C in a Nutshell, 2nd Edition

Chapter 3. Literals

In C source code, a literal is a token that denotes a fixed value, which may be an integer, a floating-point number, a character, or a string. A literal’s type is determined by its value and its notation.

The literals discussed here are different from compound literals, which were introduced in the C99 standard. Compound literals are ordinary modifiable objects, similar to variables. For a full description of compound literals and the special operator used to create them, see Chapter 5.

Integer Constants

An integer constant can be expressed as an ordinary decimal numeral, or as a numeral in octal or hexadecimal notation. You must specify the intended notation by a prefix.

A decimal constant begins with a nonzero digit. For example, 255 is the decimal constant for the base-10 value 255.

A number that begins with a leading zero is interpreted as an octal constant. Octal (or base eight) notation uses only the digits from 0 to 7. For example, 047 is a valid octal constant representing 4 × 8 + 7, and is equivalent with the decimal constant 39. The decimal constant 255 is equal to the octal constant 0377.

A hexadecimal constant begins with the prefix 0x or 0X. The hexadecimal digits A to F can be upper- or lowercase. For example, 0xff, 0Xff, 0xFF, and 0XFF represent the same hexadecimal constant, which is equivalent to the decimal constant 255.

Because the integer constants you define will eventually be used in expressions and declarations, their type is important. ...