0x00000000 hexadecimal?

Question

I had always been taught 0–9 to represent values zero to nine, and A, B, C, D, E, F for 10-15.

I see this format 0x00000000 and it doesn't fit into the pattern of hexadecimal. Is there a guide or a tutor somewhere that can explain it?

I googled for hexadecimal but I can't find any explanation of it.

So my 2nd question is, is there a name for the 0x00000000 format?

Answer 1

0x simply tells you the number after it will be in hex

so 0x00 is 0, 0x10 is 16, 0x11 is 17 etc

Answer 2

The 0x is just a prefix (used in C and many other programming languages) to mean that the following number is in base 16.

Other notations that have been used for hex include:

$ABCD
ABCDh
X'ABCD'
"ABCD"X

Answer 3

Yes, it is hexadecimal.

Otherwise, you can't represent A, for example. The compiler for C and Java will treat it as variable identifier. The added prefix 0x tells the compiler it's hexadecimal number, so:

int ten_i = 10;
int ten_h = 0xA;

ten_i == ten_h; // this boolean expression is true

The leading zeroes indicate the size: 0x0080 hints the number will be stored in two bytes; and 0x00000080 represents four bytes. Such notation is often used for flags: if a certain bit is set, that feature is enabled.

P.S. As an off-topic note: if the number starts with 0, then it's interpreted as octal number, for example 010 == 8. Here 0 is also a prefix.