[commandlinefan]

    for (int i = 0; i < strlen(s); i++) {
        s[i] ^= 0x20;
    }

[calibas]

Thank you for this universal approach. I can now toggle capitalization on/off for any character, instead of just being limited to alphabetic ones!

Jokes aside, I was kinda hoping for a good answer that doesn't rely on a Windows API or an external library, but I'm not sure there is one. It's a rather complex problem when you account for more than just ASCII and the English language.

[TZubiri]

Next up, check out our vector addition implementation of Hello+World. Spoiler alert, the result is Zalgo

[vardump]

Surely you meant:

  s[i] &= ~0x20;

We're talking about converting to upper case after all! As an added benefit, every space character (0x20) is now a NUL byte!

[account42]

Free strtok!