From WikiChip
not macro - <iso646.h> - C
< c‎ | iso646.h

The not macro, which is part of <iso646.h>, is a convenient object-like macro name that expands to the ! operator. The macro was added in Normative Addendum 1 in an effort to provide support for international character sets that might not have the ! symbols.

Synopsis[edit]

#include <iso646.h>
#define not !

Description[edit]

The not object-like macro expands to the ! operator.

Example[edit]

#include <iso646.h>

int main ()
{
    if (not(2 == 1))
        return 1;
    return 0;
}