Example: while loop

--------------------------------------------------------
-- How long to be a millionaire?
-- adapted from Skansholm, section 2.4.8, page 59
--------------------------------------------------------

with TEXT_IO; use TEXT_IO;      -- specify packages

procedure rich is

    -- declare integer and float I/O libraries
    package int_io is new TEXT_IO.INTEGER_IO( INTEGER );
    package float_io is new TEXT_IO.FLOAT_IO( FLOAT );
    use  int_io, float_io;

    -- constants and variables required
    number_of_days   : integer := 1;
    days_wage        : float   := 0.01;
    total_earnings   : float   := 0.01;
    desired_earnings : constant float := 1000000.0;

begin -- rich

    -- How many days needed, doubling income each day?
    while total_earnings < desired_earnings loop
        number_of_days := number_of_days + 1;
        days_wage      := days_wage * 2.0;
        total_earnings := total_earnings + days_wage;
    end loop;

    -- tell us the good news!
    put ("You will be a millionaire in ");
    put (number_of_days, width=>1);
    put_line ("days.");

end rich;