CODEWITHSUNDEEP
cbinary
letter Q
letter Q

Reputation: 15405

Why is 0x00000100 = 256?

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

Upvotes: 7

Views: 15182

Answers (6)

Dietrich Epp
Dietrich Epp

Reputation: 213528

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

Upvotes: 29

shas
shas

Reputation: 703

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

Upvotes: 1

Korchkidu
Korchkidu

Reputation: 4946

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

Upvotes: 8

Fiddling Bits
Fiddling Bits

Reputation: 8861

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

Upvotes: 3

trojanfoe
trojanfoe

Reputation: 122401

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.

Upvotes: 11

Basile Starynkevitch
Basile Starynkevitch

Reputation: 1

The 0x prefix means hexadecimal

Upvotes: 6

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