A leading zero is any 0 digit that comes before the first nonzero digit in a
number string in positional notation. For example, James Bond's famous
identifier, 007, has two leading zeros. When leading zeros occupy the most
significant digits of an integer, they could be left blank or omitted for the
same numeric value. Therefore, the usual decimal notation of integers does not
use leading zeros except for the zero itself, which would be denoted as an
empty string otherwise. However, in decimal fractions strictly between −1
and 1, the leading zeros digits between the decimal point and the first nonzero
digit are necessary for conveying the magnitude of a number and cannot be
omitted. Occurrence
Often, leading zeros are found on non-electronic digital displays or on
such electronic ones as seven-segment displays, that contain fixed sets of
digits. These devices include manual counters, stopwatches, odometers, and
digital clocks. Leading zeros are also generated by many older computer
programs when creating values to assign to new records, accounts and other
files, and as such are likely to be used by utility billing systems, human
resources information systems and government databases. Many digital
cameras and other electronic media recording devices use leading zeros when
creating and saving new files to make names of the equal length.
Leading zeros also present whenever the number of digits is technically fixed,
but the stored value is not large enough to result in a non-zero most significant
digit. The count leading zeros operation efficiently determines the number of
leading zero bits in a machine word. A leading zero appears in roulette in
the United States, where "00" is distinct from "0". Sports where
competitors are numbered follow this as well; a stock car numbered "07" would be
considered distinct from one numbered "7". Benito Santiago, a Major League
Baseball catcher who wore the number 09 for several years, is the only major
professional sports league player to use a jersey number with a leading zero, not
counting several who have worn the number 00. This is most common with
single-digit numbers. Advantages
Collation Leading zeros are used to make ascending
order of numbers correspond with alphabetical order: e.g., 11 comes
alphabetically before 2, but after 02. This does not work with negative
numbers, though, whether leading zeroes are used or not: −23 comes
alphabetically after −01, −1, and −22, although it is less than all of them.
Error prevention Leading zeros in a sentence also make it
less likely that a careless reader will overlook the decimal point. For example,
in modern pharmacy there is a widely followed convention that leading zeros
must not be omitted from any dose or dosage value in drug prescribing.
Likewise, just as leading zeros are mandatory, trailing zeros are forbidden.
In both cases, the reason is the same: to prevent misreading and the resultant
misdose by one or several orders of magnitude.
Fraud prevention Leading zeros can also be used to
prevent fraud by filling in character positions that might normally be empty.
For example, adding leading zeros to the amount of a check makes it more
difficult for fraudsters to alter the amount of the check before presenting it
for payment. 0 as a prefix
A prefix 0 is used in C to specify string representations of octal numbers,
as required by the ANSI C standard for the "strtol" function in the "stdlib.h"
library. Many other programming languages, such as Python 2, Perl, Ruby,
and the Unix shell bash also follow this specification for converting strings to
numbers. As an example, "0020" does not represent 2010, but rather 208 = 1610.
Decimal numbers written with leading zeros will be interpreted as octal by
languages that follow this convention and will generate errors if they contain
"8" or "9", since these digits do not exist in octal. This behavior can be
quite a nuisance when working with sequences of strings with embedded,
zero-padded decimal numbers to facilitate alphabetical sorting or when
validating inputs from users who would not know that adding a leading zero
triggers this base conversion. See also
Trailing zero 00
References