Icon Description
There are some triplet character sequences present in C & C++ to represent some special punctuation characters. The trigraph sequences are used for compatibility of source code written in ISO 646 or EBCDIC charset.

icon_underthehood.jpg
// Is this a valid statement? I can’t believe. But for compiler is valid.
??=define arraycheck(a,b) a??(b??) ??!??! b??(a??)

But when we apply trigraph sequence, the above code block became as follows.
// Wow!!! It’s a valid one…
#define arraycheck(a,b) a[b] || b[a]

Please see list of trigraph sequences below.
Trigraph Punctuation Character

??=	            #
??(                 [
??/                 \
??)                 ]
??’	            ^
??<                 {
??! 	            |
??>	            }
??- 	            ~

And one trigraph pitfall.
// Whether the following line compiles ???????/
cout << “Whether you can see this message?”;

Find your answer and take care trigraphs next time…
Thanks to Wiki for examples and the list.