Characters are Just Small Integers

In C, the char type is essentially a 1-byte integer. The mapping between the binary number in memory and the character you see on the screen is defined by the ASCII (American Standard Code for Information Interchange) table.

Understanding the Mapping

Every key on your keyboard has a corresponding ASCII value:

• 48 to 57: The digits 0 through 9.
• 65 to 90: Uppercase letters A through Z.
• 97 to 122: Lowercase letters a through z.
• 32: The Space character.
• 10: Newline (\n).
• 0: The Null Character (\0).

Why is this important?

Because characters are numbers, you can perform logic on them:

1. Checking for letters: if (ch >= 'A' && ch <= 'Z') checks if a character is an uppercase letter.
2. Case Conversion: The difference between 'A' (65) and 'a' (97) is always exactly 32.

• To lowercase: upper + 32
• To uppercase: lower - 32

1. Digit to Integer: To turn the character '5' into the actual number 5 for math, subtract the character '0'.

• '5' - '0' == 5 (because 53 - 48 == 5).

Control Characters (0-31)

These are non-printable characters used to control hardware:

• ASCII 7 (Bell): Makes your computer beep! (\a)
• ASCII 8 (Backspace): Moves the cursor back one spot. (\b)
• ASCII 9 (Tab): Inserts a horizontal tab. (\t)

Example ASCII Values

Extended ASCII and Unicode

Standard ASCII uses 7 bits (values 0-127). The 8th bit allowed for "Extended ASCII" (128-255) to include currency symbols and accented letters. Modern software uses Unicode (UTF-8), which can represent over 100,000 characters from every language on Earth. C handles Unicode through wider data types like wchar_t.

You can print the ASCII value of any character using printf("%d", 'Z');. You can print the character associated with any number using printf("%c", 90);. Try it out!