## What does the seemingly random C expression \'<:]{%>\' actually do?

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Unveiling the Enigmatic Smiley-Expression: "<:]{%>"

In the realm of programming, we often encounter intriguing constructs that invite curiosity. One such example is the following enigmatic expression: "<:]{%>".

Decoding the Mystery

Upon encountering this expression in a C program, we might be perplexed as to its purpose and meaning. Surprisingly, this expression compiles seamlessly, leaving neither errors nor warnings in its wake.

The key to unraveling this mystery lies in understanding the use of digraphs. Digraphs are pairs of characters that represent a single character or token in C . In this case, the digraphs used are:

• "<:" representing "["
• "%>" representing "}"

Lambda Expression Unmasked

Utilizing these digraphs, the expression "<:]{%>" translates to the following lambda expression:

[] {};

This lambda expression essentially represents a no-op (no operation), intended to do nothing. The corresponding symbols have these equivalents:

• "[" and "]" delimit the lambda expression.
• "{}" defines the lambda's body.

Practical Applications of Digraphs

Digraphs may seem like a relic of the past, but they still serve a valuable role in certain scenarios. For instance, some keyboards lack the dedicated keys required to type certain characters used in C , particularly graphical ones. Digraphs provide a way to compensate for such hardware or software limitations by combining characters into a single token.

Conclusion

Although rarely encountered in modern programming, the use of digraphs, as exemplified by the smiley-expression "<:]{%>", offers a glimpse into the intricacies and versatility of the C language.

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