Bits, Bytes and Variables

[Jop]

Since I now know how (wow how many -ow ) bits and bytes work, I want to know how many bits (or bytes, I don't care) VB reserves for a variable.

I mean how many bits/bytes does a string/integer/long/double/single/etc. use in the memory.
And how many numbers can be in a Integer/long/double/single/etc. so I know wich variable to use for wich sort of number.

I know for example
101 in binary = 5 (1+0+4) in decimal, but how does it work with for example 5.5? Does the computer use a few bytes for a number with decimals?
Like (0000010100000101) would be 5.5
But how does the computer know if it's a decimal or not?

_________   ________
|00000101|  |00000101|
|^integer|  |^decimal|

That'll clear some thinks up for me, thanx!

[Buzby]

From the VB help file;

The following table shows the supported data types, including storage sizes and ranges.

Data type 	Storage size	Range
Byte	1 byte	0 to 255
Boolean	2 bytes	True or False
Integer 	2 bytes	-32,768 to 32,767
Long
(long integer)	4 bytes	-2,147,483,648 to 2,147,483,647
Single 
(single-precision floating-point)	4 bytes	-3.402823E38 to -1.401298E-45 for negative values; 1.401298E-45 to 3.402823E38 for positive values
Double 
(double-precision floating-point)	8 bytes	-1.79769313486232E308 to 
-4.94065645841247E-324 for negative values; 4.94065645841247E-324 to 1.79769313486232E308 for positive values
Currency 
(scaled integer)	8 bytes	-922,337,203,685,477.5808 to 922,337,203,685,477.5807
Decimal	14 bytes	+/-79,228,162,514,264,337,593,543,950,335 with no decimal point; 
+/-7.9228162514264337593543950335 with 28 places to the right of the decimal; smallest non-zero number is 
+/-0.0000000000000000000000000001
Date	8 bytes	January 1, 100 to December 31, 9999
Object	4 bytes	Any Object reference
String 
(variable-length)	10 bytes + string length	0 to approximately 2 billion 
String
(fixed-length)	Length of string	1 to approximately 65,400
Variant
(with numbers)	16 bytes	Any numeric value up to the range of a Double
Variant
(with characters)	22 bytes + string length	Same range as for variable-length String
User-defined
(using Type)	Number required by elements	The range of each element is the same as the range of its data type.
Note   Arrays of any data type require 20 bytes of memory plus 4 bytes for each array dimension plus the number of bytes occupied by the data itself. The memory occupied by the data can be calculated by multiplying the number of data elements by the size of each element. For example, the data in a single-dimension array consisting of 4 Integer data elements of 2 bytes each occupies 8 bytes. The 8 bytes required for the data plus the 24 bytes of overhead brings the total memory requirement for the array to 32 bytes.

A Variant containing an array requires 12 bytes more than the array alone.

[Mark Sreeves]

for data type sizes have a look in the vb5 help files
there is a Data Type Summary

[Jop]

Thanks guys, but how about

Boolean 2 bytes True or False

A boolean has 2 possibilities 1 or 0, why can't you use 1 bit for it then? True (1) or False (0)?

And how about the decimal point, how do you convert it to Binary? Thanx

[ccoder]

Let's see if I can quickly answer a couple of your
questions.

From your original post:
But how does the computer know if it's a decimal or not?

A computer knows nothing, it simply follows instructions.
It is the compiler that creates the instructions in a code
(a.k.a. machine language) that the computer can follow.
The compiler creates a symbols table that contains the
memory address (actually, it's an offset value), type and
size for every variable. Based on the info in the symbols
table, the compiler generates the machine language
instructions to complete the operation. The loader
converts the offset to an actual address when the program
is launched.

Each architecture (in this case, x86) has its own
representation for real numbers. The only time I have
worked with real numbers at this level was in a BAL class
in college back in the 70’s. If you want to see how an IBM
360 stored real numbers, I can probably find an example in
one of my old texts.

From your second post:
1) A boolean has 2 possibilities 1 or 0, why can't you use
1 bit for it then? True (1) or False (0)?

A byte is the smallest addressable segment of memory.

2) And how about the decimal point, how do you convert it
to Binary?
The decimal point is ‘understood’. Part of the variable’s
memory space is allocated to the whole part of the number
and the rest is allocated to the fractional part. These
parts have names, but as I said, it’s been a while and I
forget the names. Unless you are working in assembler, you
just let the compiler 'worry' about the details.

[KillemAll]

You have to admit, they could have and should have made the boolean more efficent. I mean if you were gonna have 50 boolean variables, you would be using 100 bytes vs if you declared them as Byte you would only be using 50 bytes and then you could just use a value of 0 and 1 for true and false. It doesnt make much sense to me that they made it two bytes, but hey, they are Microsoft, what are you gonna do? hehe

Just MHO,
KillemAll

If my CS teacher is right...

Decimal points are done in the same concept as integers, etc.. In unsigned integers, the bits count from 2^0 (1) to 2^15 (32768).

In doubles, the first four bytes are for integers (positive powers of 2), and the last four bytes are for fractions (negative powers of 2).

For example, 00000000|00000000|00000000|00000111|11100000|00000000|00000000|00000000 (which can be written as 111.111, where the "." indicates the middle of the bit string) is really just

2^2 + 2^1 + 2^0 + . + 2^-1 + 2^-2 + 2^-3
= 4 + 2 + 1 + 0 + .5 + .25 + .125
= 5.875.

In this form, 5.5 can be written as 101.1 in binary.