Converting B to MB properly, or entirely wrong - c++

Question

I'm not very experienced in these things, so please try not to jump to conclusions right out the gate. Okay, so I've got a number in bytes that I've been trying to convert to mb with little consistency or success. An example is a directory I have that comes back as 191,919,191 bytes (191.919 MB) when I 'get info'.
I was curious about how to convert it myself, so here's what I learned:
Google:
1 KB = 1000 B
1 MB = 1000 KB
1 GB = 1000 MB
So far so good...
1024000 B in KB = 1024
1024 KB in MB = 1.024
This seems perfectly logical...
191,919,191 B to MB = 191.919 MB
This looks correct too, but when I go to convert my bytes to mb using mostly any code sample out there in existence I end up with something far different from friendly ol' google.
According to Princeton
SYNOPSIS:
Converting between bytes, kilobytes, megabytes, and gigabytes.
SOLUTION:
1 byte = 1 character
1 kilobyte (kb) = 1024 bytes
1 megabyte (Mb) = 1024 kb = 1,048,576 bytes
1 gigabyte (Gb) = 1024 Mb = 1,048,576 kb = 1,073,741,824 bytes
So with this information:
191.919 mb / (1024000) = 187.421 B
I've also seen conversions like this:
191.919 mb / (1024 * 1024) = 183.028 B
WTF? is this stuff just made up as we go along, or is there some standard way of getting the real file size in mb from bytes? I'm completely lost and confused now because of this conflicting information. I have no real idea of who is right or wrong with this, or if I'm just completely missing something.
I have code like this:
UInt32 fileSize = 191919191; // size in bytes
UInt32 mbSize = fileSize / 1024000; // do conversion
printf(#"%u MB",(unsigned int)mbSize); // result:
Which outputs:
187 MB
So how in the world can 191,919,191 bytes = 191 MB?

Answer 1

Just to summarise...
The official, SI standardised, correct use of the prefixes is that kilo = 10^3 = 1000, mega = 10^6 = 1000000 and so on. The abbreviations are K, M, G etc.
There is a separate set of prefixes for the digital world where kibi = 2^10 = 1024, mebi = 2^20 = 1048576 and so on. The abbreviations are Ki, Mi, Gi and so on.
In popular usage the abbreviations K, M, G etc are slightly vague, and sometimes understood to mean one thing, sometimes the other.
The bottom line is that whenever it matters, you have to take extra care to know which you're using. Some documentation will not have taken that care, and can be very misleading. I don't see this ambiguity changing any time soon.