Is 0 an octal or a decimal in C?
CLanguage LawyerLiteralsOctalC Problem Overview
I have read this. It's octal in C++ and decimal in Java. But no description about C?
Is it going to make any difference if 0 is octal or decimal? This is the question asked by my interviewer. I said no and I explained that it is always 0 regardless whether it is octal or decimal.
Then he asked why is it considered as octal in C++ and decimal in Java. I said it's the standard. Please let me know what is it in C? Will it make any difference? Why are they different in different standards?
C Solutions
Solution 1 - C
It makes little difference, but formally the integer constant 0 is octal in C. From the C99 and C11 standards, 6.4.4.1 Integer constants
> integer-constant:
> decimal-constant integer-suffixopt
> octal-constant integer-suffixopt
> hexadecimal-constant integer-suffixopt
>
> decimal-constant:
> nonzero-digit
> decimal-constant digit
>
> octal-constant:
> 0
> octal-constant octal-digit
>
> hexadecimal-constant:
> ...
> ...
Solution 2 - C
Octal.
>###C11 §6.4.4.1 Integer constants
> octal-constant: 0 octal-constant octal-digit
And this is true since C89 §3.1.3.2.
Solution 3 - C
> Then he asked why is it considered as octal in C++ and decimal in Java
For sake of completeness, worth mentioning Java specs as well. From Java Language Specification 3.10.1:
> > > DecimalNumeral: > 0 > NonZeroDigit Digitsopt > NonZeroDigit Underscores Digits > > A decimal numeral is either the single ASCII digit 0, representing the integer zero, or consists of an ASCII digit from 1 to 9 optionally followed by one or more ASCII digits from 0 to 9 interspersed with underscores, representing a positive integer.
> > > OctalNumeral: > 0 OctalDigits > 0 Underscores OctalDigits > > An octal numeral consists of an ASCII digit 0 followed by one or more of the ASCII digits 0 through 7 interspersed with underscores, and can represent a positive, zero, or negative integer.
As you can see, a bare 0 is considered as decimal.
Whereas any (non-empty) sequence of digits preceded by 0 is considered as octal.
Interestingly enough, from that grammar:
0is decimal- but
00is octal
Solution 4 - C
From the C Standard (6.4.4.1 Integer constants)
octal-constant:
0
octal-constant octal-digit
In fact there is no any difference for zero because zero is a common digit for octal, decimal and hexadecimal numbers. It has meaning only when a number has other digits apart from the single (leading) zero.
Take into account that there are no such integral types as decimal, octal or hexadecimal.
Solution 5 - C
It's an octal. See section 6.4.4.1 Integer constants of the N1570 draft:
integer-constant:
decimal-constant integer-suffixopt
octal-constant integer-suffixopt
hexadecimal-constant integer-suffixopt
decimal-constant:
nonzero-digit
decimal-constant digit
octal-constant:
0
octal-constant octal-digit
hexadecimal-constant:
hexadecimal-prefix hexadecimal-digit
hexadecimal-constant hexadecimal-digit
hexadecimal-prefix: one of
0x 0X
nonzero-digit: one of
1 2 3 4 5 6 7 8 9
octal-digit: one of
0 1 2 3 4 5 6 7
hexadecimal-digit: one of
0 1 2 3 4 5 6 7 8 9
a b c d e f
A B C D E F
integer-suffix:
unsigned-suffix long-suffixopt
unsigned-suffix long-long-suffix
long-suffix unsigned-suffixopt
long-long-suffix unsigned-suffixopt
unsigned-suffix: one of
u U
long-suffix: one of
l L
long-long-suffix: one of
ll LL
Also:
> 3. A decimal constant begins with a nonzero digit and consists of a sequence of decimal digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed by a sequence of the decimal digits and the letters a (or A) through f (or F) with values 10 through 15 respectively.
Solution 6 - C
I think it depends on compiler implementation. We have to see the source code to determine whether it flags a "0" constant as octal or not. I can define the non-octal reason in this way: Octals has "0" prefix. But there is no prefix. If the constant is 00, then it IS octal - "octal Zero" :)