The while / until statements may never execute the
control strucuture at all if the control expression evaluates the
right way the first time.
There are times that you want to make sure the control structure
executes at least one time, for example if the control expression is
not valid until the control structure has performed some operation.
You can move the while / until expression to the
end of the control structure with the do operator.
Just like in 'C' or 'C++', give the expression a terminating
semicolon in this case.
Example:
do {
some_statement;
some_statement;
some_statement;
} while ( expression );
Example:
do {
some_statement;
some_statement;
some_statement;
} until ( expression );