When to use a semicolon in Pascal (idea)

If you follow StrawberryFrog's advise, I'm sure it'll work fine in Delphi, but many traditional pascal compilers will consider that a syntax error. Pascal's semicolon rules are not any more complex than C. They're just different.

In C, the semicolon is a statement terminator, and sometimes is itself a null statement, and so you can have as many as you want in a row with no actual code between. In fact, if you want to put a label before a close brace, you must put a semicolon after the label to make a null statement. (The label is a goto target, so you need a statement there to be the target.)

In pascal, the semicolon is a statement separator, and only goes between statements. In some (traditional) pascal compilers, there is no null statement, and so even one extra semicolon is actually a syntax error, including before an end. Many pascal compilers will allow this, however, which makes them a lot easier to deal with.

I'll steal the examples from above, and translate to C, to show the difference:

Single statement if-then-else:

printf("N is no");
if (n == 0)      // parens optional in pascal, required in C
  printf("w");  // semicolon required in C, error in pascal!!!
else
  printf("t");
printf(" zero."); // semicolon added

This is the one that confuses most beginning students, and is the example left out of StrawberryFrog's wu above.

if-then-else using blocks in pascal

if n = 0 then // parens optional -- left out
 begin
  ShowMessage('N is now zero');
  Result := 1;    // some compilers will take this
 end    // never use a semicolon before else!
else
...

if-then-else using blocks in C

if (n == 0)   // parens required
 {
  ShowMessage("N is now zero');
  Result = 1;    // required
 }    // semicolon not needed after a brace!
else
 {
  ShowMessage("N is not zero'); // required
 }

Actually, in the C example, putting a semicolon after the close brace would put a null statement between the then statement and the else keyword, which would be a syntax error, just like in pascal, but for a different reason.

I think StrawberryFrog's point is that if you always use begin and end, and your compiler takes ; as a null statement, then it is about the same as C. Personally, I find the single statement version of if-then-else more elegant when applicable, and the inconsistency of not putting a ; after every statement is a wart in the elegance. It's a bigger wart if you have a compiler that also doesn't like ; immediately before end statements, but then at least it is consistent.