ASCII (American Standard Code for Information Interchange) is a character encoding standard for electronic communication. It assigns a unique numerical value to letters, digits, punctuation marks, and control signals, allowing computers to store and exchange text.

Key Features

• 7-Bit Standard: The original ASCII uses 7 bits to represent 128 unique characters.
• Universal Basis: It forms the foundation for modern encodings like Unicode (UTF-8).
• Sequential ordering: Letters and numbers are ordered sequentially, making sorting and manipulation easy.

How ASCII Works

ASCII maps human-readable characters to integer values. The standard set uses 7 bits ($2^7 = 128$ characters).

Key Character Ranges

Character Groups

1. Control Characters (0-31)

These were originally designed to control hardware devices like teletype machines and printers.

• NULL (0): Represents 'nothing'. Used to terminate strings in C/C++.
• Line Feed (10): Moves the cursor to the next line.
• Carriage Return (13): Moves the cursor to the start of the line.

2. Printable Characters (32-126)

These include all the numbers, letters, and symbols you see on your keyboard.

• Digits: '0' starts at 48.
• Letters: 'A' starts at 65, 'a' starts at 97.

3. Extended ASCII (128-255)

Standard ASCII only uses 7 bits. Computers work in 8-bit bytes. The "Extended ASCII" set uses the 8th bit to add another 128 characters, such as mathematical symbols ($\div$, $\pm$) and accented letters (é, ñ).

Important ASCII Calculations

1. Case Conversion

The difference between an uppercase letter and its lowercase equivalent is exactly 32.

   'A' (Decimal 65)  = 0100 0001
+  32  (Decimal 32)  = 0010 0000
--------------------------------
   'a' (Decimal 97)  = 0110 0001
    

2. Digit vs. Value

The character '0' is not the same as the value 0. To convert an ASCII digit to its integer value, subtract 48.

   char input = '5';    // ASCII value is 53
   int value = input - 48; // 53 - 48 = 5
    

Frequently Asked Questions (FAQ)