Why the following do-while loop is valid?

Question

The loop is as follows:

do;
while(1);

Why the above loop is not giving a syntax error?

I am using mingw gcc compiler

Answer 1

That code looks like it was written to obfuscate its meaning but if we look at the draft C99 standard section 6.8.5 Iteration statements, the grammar for do while is:

do statement while ( expression ) ;

and statement can be an expression statement which in turn can be a null statement which is what ; is. So it is the same as:

do
  ;
while(1);

we can see from section 6.8.3 Expression and null statements paragraph 3 says:

A null statement (consisting of just a semicolon) performs no operations.

Answer 2

do
    ; //nop
while(1);

Now it is more readable :)

---

Note that the ; is a Null Statement.

Answer 3

This is a single statement do-while loop equivalent to

do
    no_op(); // do nothing
while (1);

or

do {
}
while (1);

Answer 4

Personally, I hate null statements and I'd be perfectly happy to have them removed from the standard.

My preferred form would be

do continue;
while (1);

Answer 5

Because it is an infinite loop with an empty statement ;.

do
{
   ;

}while(1);