Lecture #3 – September 3, 2007

We briefly reviewed the printout of Use_Date_with_output.adb

All instantiations for reading and writing are of the form:

package identifier is new ada.text_io.type_io (data type);

We remembered that you can’t execute a package body.

We learned that in month_type’first the apostrophe is read as “tick” and that ’first and ’last are attributes of an enumerated type (such as month_type) as are ’succ and ’pred.

We learned that the last element in an enumerated type definition has no successor (’succ) and that the first element in an enumerated type definition has no predecessor (’pred)

We changed the enumerated list of months in date.ads and recompiled play_with_enumerated_types.adb to use the new version but didn’t have to change anything in it.

We expanded on procedure play_with_enumerated_types.adb by adding exception handling

We learned how to handle two different kinds of errors: constraint_error and data_error.

We learned that data_error is in the ada.io_exceptions package and needs a with statement

We discussed the three types of loop statements and learned how to use the Ada95 reference manual (see excerpt below)

5.5 Loop Statements

1

   A loop_statement includes a sequence_of_statements that is to be executed repeatedly, zero or more times.

Syntax

2

loop_statement ::=
   [loop_statement_identifier:]
      [iteration_scheme] loop
sequence_of_statements
end loop [loop_identifier];

3

iteration_scheme ::= while condition
   | for loop_parameter_specification

4

loop_parameter_specification ::=
defining_identifier in [reverse] discrete_subtype_definition

5

If a loop_statement has a loop_statement_identifier, then the identifier shall be repeated after the end loop; otherwise,

there shall not be an identifier after the end loop.

We saw that the loop control variable of a for loop may not be modified by the programmer within the loop

We saw that if we have a variable declared as i outside a for loop and the loop control variable is also an i, then the two variables are independent and the i outside the loop is only accessible outside the loop and the loop control variable i is only accessible inside the loop.

We learned that exception handlers go at the end of a block; that they can be embedded in a loop but then the loop should have a begin and an end in addition to the loop … end loop

We learned that you can have multiple exception handlers together in a procedure but each follows a when => statement and the word exception only appears once in that case.