Why does #define not require a semicolon?

Question

I was writing some test code in C. By mistake I had inserted a ; after a #define, which gave me errors. Why is a semicolon not req

Answer 1

The second version does not define a constant as far as the language is concerned, just a substitution rule for a block of text. Once the preprocessor has done it's job, the compiler sees

char buffer [256;];

which is not syntactically valid.

The moral of the story: prefer the const int MAX_STRING = 256; way as that helps you, the compiler, and the debugger.