The iso646.h header in c was defined as part of the c99 standard .

It defines replacement for equality , boolean and bitwise operators . For example instead of using the bitwise && operator , the and replacement can be used .

iso646.h operators replacements do not work in string or character literals .

A trigraph in c is formed of three characters . The first two characters are interrogation marks ?? , and the last character represent a character .

In this tutorial we will explain what is a trigraph in c .