## What\'s Hiding Behind the \'Smile\' in This C Code: A Digraph Mystery?

Understanding the Cryptic Smiley-with-Beard Expression

In the peculiar code snippet below, a puzzling smiley-with-beard expression appears:

int main() {
  <:]{%>; // smile!
}

What is the nature of this expression, and how does it contribute to the program's behavior?

Unveiling the Digraph Magic

The key to understanding this oddity lies in the concept of digraphs. Digraphs are sequences of characters that represent a single token in C . In this case, the digraphs used are:

• <: corresponds to [
• %> corresponds to }

Lambda Expression in Disguise

Using digraphs, the expression "<:]{%>" can be interpreted as the following lambda expression:

[] {};

This lambda expression effectively does nothing.

Historical Significance of Digraphs

Digraphs were introduced in C to provide an alternative representation for certain characters that might be unavailable on specific keyboards. They were particularly useful in the early days of computing when certain graphical characters were lacking.

By combining the characters that make up a digraph, compilers are able to treat them as a single token. This flexibility allows for compatibility even when keyboards or other hardware and software have limited character support.

Conclusion

While digraphs may not be as necessary in today's modern computing environment, they continue to serve as a historical reminder of the ingenuity and flexibility inherent in C . By employing digraphs, programmers were able to overcome hardware limitations and ensure code portability across a variety of platforms.

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