// Clause: 7.4 — The argument to classification functions shall be EOF or representable as unsigned char; otherwise UB.
#include <ctype.h>
#include <stdio.h>
int main(void){
    int c = 256; // outside unsigned char on 8-bit char
    int r = isalpha(c); // UB
    printf("%d\n", r);
    return 0;
}