What do numbers using 0x notation mean?

Literals that start with 0x are hexadecimal integers. (base 16)

The number 0x6400 is 25600.

6 * 16^3 + 4 * 16^2 = 25600

For an example including letters (also used in hexadecimal notation where A = 10, B = 11 ... F = 15)

The number 0x6BF0 is 27632.

6 * 16^3 + 11 * 16^2 + 15 * 16^1 = 2763224576    + 2816      + 240       = 27632

c integer hex notation

In C and languages based on the C syntax, the prefix 0x means hexadecimal (base 16).

Thus, 0x400 = 4×(16²) + 0×(16¹) + 0×(16⁰) = 4×((2⁴)²) = 2² × 2⁸ = 2¹⁰ = 1024, or one binary K.

And so 0x6400 = 0x4000 + 0x2400 = 0x19×0x400 = 25K

c integer hex notation

It's a hexadecimal number.

0x6400 translates to 4*16^2 + 6*16^3 = 25600

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