Why are hexadecimal numbers prefixed with 0x

Question

Why are hexadecimal numbers prefixed as 0x   I understand the usage of the prefix but I don t understand the significance of why 0x was chosen

User · Accepted Answer

Short story  The 0 tells the parser it s dealing with a constant  and not an identifier reserved word   Something is still needed to specify the number base  the x is an arbitrary choice   Long story  In the 60 s  the prevalent programming number systems were decimal and octal     mainframes had 12  24 or 36 bits per byte  which is nicely divisible by 3   log2 8    The BCPL language used the syntax 8 1234 for octal numbers  When Ken Thompson created B from BCPL  he used the 0 prefix instead  This is great because   an integer constant now always consists of a single token  the parser can still tell right away it s got a constant  the parser can immediately tell the base  0 is the same in both bases   it s mathematically sane  00005    05   and no precious special characters are needed  as in  123     When C was created from B  the need for hexadecimal numbers arose  the PDP-11 had 16-bit words  and all of the points above were still valid  Since octals were still needed for other machines  0x was arbitrarily chosen  00 was probably ruled out as awkward    C  is a descendant of C  so it inherits the syntax

User · Answer

Note   I don t know the correct answer  but the below is just my personal speculation   As has been mentioned a 0 before a number means it s octal   04524    octal  leading 0   Imagine needing to come up with a system to denote hexadecimal numbers  and note we re working in a C style environment   How about ending with h like assembly   Unfortunately you can t - it would allow you to make tokens which are valid identifiers  eg  you could name a variable the same thing  which would make for some nasty ambiguities   8000h    hex FF00h    oops - valid identifier   Hex or a variable or type named FF00h    You can t lead with a character for the same reason   xFF00    also valid identifier   Using a hash was probably thrown out because it conflicts with the preprocessor    define      FF00    invalid preprocessor token    In the end  for whatever reason  they decided to put an x after a leading 0 to denote hexadecimal   It is unambiguous since it still starts with a number character so can t be a valid identifier  and is probably based off the octal convention of a leading 0   0xFF00    definitely not an identifier

User · Answer

It s a prefix to indicate the number is in hexadecimal rather than in some other base  The C programming language uses it to tell compiler    Example   0x6400 translates to  6 16 3   4 16 2   0 16 1  0 16 0   25600  When compiler reads 0x6400  It understands the number is hexadecimal with the help of 0x  term   Usually we can understand by  6400 16 or  6400 8 or whatever      For binary it would be   0b00000001  Hope I have helped in some way   Good day

User · Answer

The preceding 0 is used to indicate a number in base 2  8  or 16   In my opinion  0x was chosen to indicate hex because  x  sounds like hex   Just my opinion  but I think it makes sense   Good Day

[c] Why are hexadecimal numbers prefixed with 0x?

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