🧮 Foundations — Before C

Text: ASCII, Unicode & UTF-8

⏱ 12 min · free interactive lesson · quizzes, visualizations & a real compiler

Computers only store numbers — so what is the letter 'A'? It's just the number 65, by agreement. That agreement is called a character encoding, and it's the bridge between bytes and human text.

ASCII: the original deal (1963)

ASCII assigns 0–127 to English letters, digits, punctuation, and control codes. The layout is delightfully hackable:

• '0'–'9' are 48–57 → digit - '0' converts a digit character to its value
• 'A'–'Z' are 65–90, 'a'–'z' are 97–122 → exactly 32 apart, one bit! c | 0x20 lowercases a letter
• 0–31 are control codes: '\n' = 10 (newline), '\t' = 9 (tab), '\0' = 0 (the string terminator — hugely important in C)

#include <stdio.h>

int main(void) {
    char c = 'A';
    printf("'%c' is %d\n", c, c);        /* chars ARE numbers  */
    printf("'%c' + 1 = '%c'\n", c, c + 1);
    printf("'7' - '0' = %d\n", '7' - '0');   /* digit trick     */
    printf("'Q' | 0x20 = '%c'\n", 'Q' | 0x20); /* lowercase bit */
    return 0;
}

$ gcc ascii.c -o ascii && ./ascii
'A' is 65
'A' + 1 = 'B'
'7' - '0' = 7
'Q' | 0x20 = 'q'

Unicode: one number for every character ever

ASCII has no é, no 中, no 🎉. Unicode fixes this by assigning a code point to every character in every language — over 150,000 so far, written like U+1F600. But code points are abstract numbers; we still need to store them as bytes. Enter UTF-8, the encoding that won the internet:

• Code points 0–127 (plain ASCII) → 1 byte, identical to ASCII. Every ASCII file is already valid UTF-8!
• Latin accents, Greek, Cyrillic → 2 bytes · CJK characters → 3 bytes · emoji → 4 bytes

Type below and watch each character become bytes:

▶ This spot has an interactive enc widget — open the interactive lesson to play with it.