How to compile and link simple application?

[4544fa8d]

On Monday, 8 April 2019 at 18:41:00 UTC, Adam D. Ruppe wrote:
> Did you put your code inside a main() function?

I want to make constant with path to directory containing 
executable. This line is above main():
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const ROOT_DIR = dirName(thisExePath());
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This is not allowed? :O