FOR STATEMENT

for(expr1; expr2; expr3) statement;

Execute 'expr1' once. Then, while 'expr2' returns a non-zero value,
execute 'statement'. Every time 'statement' has been executed, or a 'continue'
statement has been executed, execute 'expr3' before next loop.

A 'break' in the 'statement' will terminate the loop. A 'continue' will
continue the execution from the beginning of the loop.

example:

    for (x=0; x<11; ++x) {
      write(x+" ");
    }

will give the following output:

0 1 2 3 4 5 6 7 8 9 10