how is 65 translated to 'A' character?

Question

In ASCII, i wonder how is 65 translated to 'A' character? As far as my knowledge goes, 65 can be represented in binary but 'A' is not. So how could this conversion happen?

Answer 1

Everything in a computer is stored as a number. It's how software interprets those numbers that's important.

ASCII is a standard that maps the number 65 to the letter 'A'. They could have chosen 66 or 14 to represent 'A', but they didn't. It's almost arbitrary.

So if you have the number 65 sitting in computer memory somewhere, a piece of code that treats that piece of memory as ASCII will map the 65 to 'A'. Another piece of code that treats that memory as an entirely different format may translate it to something else entirely.

HTH,
Kent

Answer 2

'A' IS 65. It's just that your display device knows that it should display the value 65 as an A when it renders that value as a character.

Answer 3

It is just a 'definition'. ASCII defines the relationships between integer values and characters. For implementation, there is a table (you can't see it) that does this translation.

EDIT: Computers just 0/1. A stream of characters is just a bunch of 0/1 streams: 0110010101... There is a contract between human and computer: 8 bits are represented as a character (okay, there are Unicode, UTF-8 and etc). And, 'A' is 65 and so on.

In C/C++ and any other languages, strings are just handled like integer arrays. Only when you need to display strings, that numbers are 'translated' into character. This translation is done by either hardware or software:

• If you write a function that draws character, you're responsible to draw 'A' when the input is 65.
• In the past, say that we're in DOS, the computer draws 'A' on the number 65. That relationship is usually stored in the memory. (At that time where no graphics, only text, this table can be tweaked to extend characters. I remember Norton DOS utilities such as NDD/NCD changed this table to draw some special characters that were not in the regular ASCII code.)

You may see this sort of contract or definition in everywhere. For example, assembly code. Your program will be eventually translated into machine code: that is also just a bunch of 0 and 1. But, it is extremely hard to understand when only 0 and 1 are shown. So, there is a rule: say 101010 means "add", 1100 means "mov". That's why we can program like "add eax, 1", and it'll be ultimately decoded into 0/1s.

Answer 4

The ASCII table is just an agreed upon map of values and characters.

When the computer is instructed to write a character represented by a number to the screen it just finds the numbers corresponding image. The image doesn't make any sense to the computer, it could be an image that looks like an 'A' or a snowman to the user.

Answer 5

Its based on a lookup table invented back in the 60's.

Answer 6

Everything in a computer is binary. So a string in C is a sequence of binary values. Obviously that is not much use to humans, so various standards developed, where people decided what numerical values would represent certain letters. In ASCII the value 65 represents the letter A. So the value stored is 65, but everyone knows (because they have read the ASCII spec) that value corresponds to the letter A.

For example, if I am writing the code to display text on the screen, and I receive the value 65, I know to set certain pixels and delete other pixels, so that pixels are arranged like:

  @
 @ @
@@@@@
@   @
@   @

At no point does my code "really know" that is an "A". It just knows that 65 is displayed as that pattern. Because, as you say, you cannot store letters directly, only binary numbers.

Answer 7

So how could this conversion happen?

This conversion is merely called character encoding. The computer only understands bytes and humans (on average =) ) only understands characters. The computer has roughly said a mapping of all bytes and all characters which belongs to those bytes so that it can present the data in a human friendly manner. It's all software based (thus not hardware based). The operating system is usually the one who takes care about this.

ASCII is one of the oldest character encodings. Nowadays we should be all on UTF-8 to avoid Mojibake.