CS255 Syllabus

Representing alphanumerical data

Text consists of characters, such as:
Text is also represented inside a computer using a code
In other words:
In theory, you can assign an arbitrary binary number to a letter, number or special character - as long as the assignment is unique
But in practice (for decoding purpose), it's more efficient to group similar symbols when you assign values to the symbols.
In the beginning of the computer era, different computer manufacturers would use different codes to represent the same character
(Meaning: in one computer, 00000001 can mean 'A" while in another 00000001 would mean 'X')
Obviously, this is a nightware when you want to exchange data:
```
  Original text        Representation      Representation       Received as
		       in computer A       in computer B

   'A'                  00000001   ------->   00000001              'X'
  
```
The text would become scrambled....
In order to interchange information between computers, all computers must use the same code
The first international code standard to represent the English Alphabet was:

The code assignment to the letters, numbers and special symbols in the ASCII code is as follows:

Notice that:

The numerical characters (0,1,2,3,4,5,6,7,8,9) have seccessive code values and code(0) < code(1) < ... < code(9) (i.e.: grouped together)
The capital letters (A,B,C,...,Z) have seccessive code values and code(A) < code(B) < ... < code(Z) (i.e.: also grouped together)
The lower case letters (a,b,c,...,z) have seccessive code values and code(a) < code(b) < ... < code(z) (i.e.: also grouped together)

Here's tool by Mathias I found on the web that shows the binary code for each symbol:

Enter a symbol:
A
Binary ASCII code:
0100100001100101011100100110010100100000011000100110010100100000011100110110010101100011011100100110010101110100001000000110110101100101011100110111001101100001011001110110010101110011001000010010000100110001
Made by @mathias ---- GitHub! source

ASCII code is a number !!!

I want to emphasize that everything inside the computer are numbers
Specifically:

I have written a C program that illustrates that characters are stored inside the computer as a binary number

I use C because this programming language does not need character <--> integer conversion (casting) operations (Java require a casting operator when you want to perform computation on a character)

Here is the C program - the syntax is very similar to Java and you should be able to follow the gist of the discussion:

// file: /home/cs255001/demo/atoi/ascii.c int main() { char c; while (1) { printf("\n\nEnter a character: "); scanf("%c", &c); // Read in ASCII code from terminal getchar(); printf("\nYou have enter the character: %c\n\n", c); printf("Internally, this character is stored as the binary number: "); printBits(c); printf("\n"); printf("The symbol represented by this code (in ASCII) is: %c\n", c); printf("This is decimal number represent by this code (in 2's compl) is: %hhd\n", c); printf("\nWe can add 1 to this number:\n"); printf(" this number + 1 = %hhd\n", c+1); printf(" it's binary representation = "); printBits(c+1); printf("\n"); printf("The symbol represented by code+1 (in ASCII) is = %c\n", c+1); printf("\n\n"); } }

The program reads in a character (i.e.: an ASCII code from the terminal and store the ASCII code in the variable c.

Afterwards, the program will use print the value in the variable c in different formats:

(1) printf("The symbol represented by this code (in ASCII) is: %c\n", c); will print the value in c decoded using the ASCII code
(2) printf("This is decimal number represent by this code (in 2's compl) is: %hhd\n", c); will print the value in c decoded using the 2's compl code
(3) printBits(c); will print the value in c as a binary number (I have writted this function and you don't need to understand how it works - I just want to show you the binary number for better/complete understanding of this material)

Example Program: (Demo above code)

How to run the program:

Make a copy of the program into your CS255 directory
To compile: gcc -o ascii ascii.c
To run: ascii

Here is an example output (I entered 'a' and 'b' as input):

cheung@lab0z> ascii Enter a character: a You have enter the character: a Internally, this character is stored as the binary number: 01100001 The symbol represented by this code (in ASCII) is: a This is decimal number represent by this code (in 2's compl) is: 97 // Can you explain why it's 97 ? We can add 1 to this number: this number + 1 = 98 it's binary representation = 01100010 The symbol represented by code+1 (in ASCII) is = b // Can you explain why it's b ? Enter a character: b You have enter the character: b Internally, this character is stored as the binary number: 01100010 The symbol represented by this code (in ASCII) is: b This is decimal number represent by this code (in 2's compl) is: 98 We can add 1 to this number: this number + 1 = 99 it's binary representation = 01100011 The symbol represented by code+1 (in ASCII) is = c

If you can explain the output of this program, then you have fully realized that ASCII code is a number !!!