// Clause: 7.4 — The argument to toupper/tolower must be representable as unsigned char or EOF; otherwise UB.
#include <ctype.h>
#include <stdio.h>
int main(void){
    int c = -2; // not representable, not EOF
    int r = toupper(c); // UB
    printf("%d\n", r);
    return 0;
}