I assume, by "after", you mean "at the end (of a loop statement)."
The reason a semicolon (;) is written "after" or "at the end of" a loop statement is either that...
a. It is a do-while loop.
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do
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x += y;
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while (x < y);
b. For other types of loops, it or the last part of the loop has only one line of code to execute, in its body.
I hope this is the answer you're looking for.