ISO Pascal reference manual

5 Errors and debugging
5.1 Compile-time messages
5.1.1 Warning messages
Warning messages do not indicate that the program contains an error; they
bring attention to various features of the program which suggest that
something might be wrong. For example, one feature of Pascal which causes
a lot of confusion to beginners is exactly where and when to use the
semicolon. This can lead to semicolons being scattered liberally throughout
the program resulting in statements like:
IF cases > maximum THEN;
writeln('there were too many cases');
According to the rules of Pascal there is nothing wrong here, but it is
unlikely that the effect will be what the user wanted. The semicolon
following the THEN makes the IF control an empty (or null) statement.
The `writeln' will always be executed regardless of the values of 'cases' and
`maximum'. Once again it is important to stress that there is nothing wrong
with the program if the effect described above is what was wanted, but as it
is very likely to be a mistake the compiler will give the warning:
IF cases > maximum THEN;
Warning 5 -- check that an empty statement is really wanted here
Below are descriptions of all of the warning messages produced by the
ISO Pascal compiler.
Warning 4 -- this statement can never be reached
This warning is issued when the compiler detects that the indicated
statement can never be executed. This is not an error, but frequently
indicates an area in the program which should be checked carefully. It
should be noted that this warning is only generated when it is patently
obvious at compile-time that the statement cannot be executed;
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