Why is 0x00000100 = 256?

Question

Shouldn't 0x00000100 = 4.

I understand that 0x00000001 = 1 since 2^0 and 0x00000010 = 2 since 2^1. What is wrong with my thinking?

initVariable(&variable1, "variable1", "1, 2, 3", 0x00000100);

assertIntegerEquals(variable1.address, 4); // 0x00000100 = 4?

My assertion fails because it says that 256 != 4

`0x` is the prefix commonly used for hexadecimal (base-16) numbers, not binary (base-2). Also, 0x00000010 is 16 since 16^1. — Daniel Kamil Kozar, Nov 20 '13 at 17:28
@jonnh, 00000100 is 8. But the OP is talking hex: 0x00000010 is 16, not 2. — Joe, Nov 20 '13 at 17:30
And by 8, I mean 4. 0001 = 1, 0010 = 2, 0100 = 4, 1000 = 8. :) — Joe, Nov 20 '13 at 17:43
@Joe: Again, at least in C `0010` is `8` and `0100` is `64` and `1000`is `1000` is `1000`, same for `1`. — alk, Nov 20 '13 at 17:48
@alk, yes, for octal interpretation. My point is: the numbers in the OP's question are shown as hex but he's interpreting as binary. — Joe, Nov 20 '13 at 18:14

score 29 · Accepted Answer · edited Sep 27 '19 at 21:29

29

Numbers that begin with 0x are interpreted as hexadecimal (base 16) in C.

So 0x10 == 16, and 0x100 == 256, 0x10000 == 65536, etc.

Powers of two are:

2⁰ = 0x1
2¹ = 0x2
2² = 0x4
2³ = 0x8
2⁴ = 0x10
2⁵ = 0x20
2⁶ = 0x40
2⁷ = 0x80
2⁸ = 0x100

edited Sep 27 '19 at 21:29

S.S. Anne

15,171
8
38
76

answered Nov 20 '13 at 17:29

Dietrich Epp

205,541
37
345
415

score 11 · Answer 2 · edited May 23 '17 at 12:25

11

No, the 0x means hexadecimal (i.e. base-16) and not binary, which is what you seem to be confusing it with.

If you want to use binary literals in your code, then see this SO question, which mentions the gcc extension that allows 0b00000100 to be used to represent 4 in binary.

edited May 23 '17 at 12:25

Community

1
1

answered Nov 20 '13 at 17:28

trojanfoe

120,358
21
212
242

Korchkidu · Answer 3 · 2013-11-20T17:51:41.640

8

0x00000100 is in base-16 because 0x prefix means you are using hexadecimal notation.

So 0x00000001 = 1*16⁰ = 1, 0x00000010 = 1*16¹, 0x00000100 = 1*16² = 256 and 0x00000123 = 1*16² + 2*16¹ + 3*16⁰ = 256 + 32 + 3 = 291

To play with base-2, base-10 and base-16 notation, you can try this site: http://www.mathsisfun.com/binary-decimal-hexadecimal-converter.html

edited Nov 20 '13 at 17:51

answered Nov 20 '13 at 17:29

Korchkidu

4,908
8
49
69

That is indeed a nice answer. – cafebabe1991 Mar 14 '18 at 08:36

score 6 · Answer 4 · answered Nov 20 '13 at 17:28

6

The 0x prefix means hexadecimal

answered Nov 20 '13 at 17:28

Basile Starynkevitch

223,805
18
296
547

score 3 · Answer 5 · answered Nov 20 '13 at 17:31

3

0x00000100 (hex) = 0000 0000 0000 0000 0000 0001 0000 0000 (binary) = 256 (decimal)

answered Nov 20 '13 at 17:31

Fiddling Bits

8,712
3
28
46

score 1 · Answer 6 · answered Sep 24 '15 at 12:36

1

0x prefix is hexadecimal 0x00000100 = 256 base 16

00000100 = 000001²0¹0⁰

= 1 * 16² + 0*16¹ + 0*⁰

=1 * 256 + 0*16 + 0*1

= 256 + 0 + 0

=256

answered Sep 24 '15 at 12:36

shas

703
2
8
31

Why is 0x00000100 = 256?

6 Answers6