Numeric constants are by default specified in decimal units. Octal and hexadecimal constants are specified using a leading 0 and 0x (or 0X), respectively. Thus, the following are equivalent: 15, 017, 0xf. Constants can be specified to be a longint by using a trailing l or L. Otherwise, their type is integer.
Floating point values can contain a decimal point (.) and an exponent (e or E). For example, 0.001 and 1e-3 are equivalent. By default, floating point constants are of type float; a double is specified by using a trailing l or L.
Character constants are delimited by single quotes. For example, the character a is specified by 'a'. A list of special characters is shown in Table 2.
Table 2: Special Characters in ZPL.
Other ASCII characters can be specified numerically by using the octal
and hexadecimal escape sequences to specify octal and hexadecimal bit
sequences. For example, ' 
x07' specifies the ASCII character whose numeric value is 7 in
hexadecimal (this happens to be the bell character).
String constants are delimited by double quotes ("). String constants
may not span multiple lines, but consecutive string constants are
automatically concatenated by the compiler to represent a single long
string constant. Thus, the following are equivalent:
"hello world"
"hello " "world".