Thursday, February 21 Week 6

Chapter 5

Student Notes

Objectives

the Math library

Writing functions

Writing Packages

1. mathematical functions in Ada

· Ada provides many useful functions for math in a packages called Ada.Numerics.Elementary_Functions

· Ada.Numerics.Elementary_Fuctions.Sqrt(X => SomeFloat);

· The name of SQRT’s float parameter is X

2. Writing function declarations

· In general, a function is written so as to require the caller to supply some values to it. When called, the function performs its desired computation and then a result to the calling program.

· The line indicating the name of the function, the expected parameters, and the returned are called the or

· Here is one you have seen before in chapter 4:

FUNCTION Year (date : time) RETURN Year_Number;

We could also declare

FUNCTION Maximum (Value1, Value2 : Integer) RETURN Integer;

3. Calling a function

·

·

· ThisYear : Ada.Calendar.Year_Number;

RightNow : Ada.Calendar.Time;

If we declare these two variables, we can then call the function Year inside our program like this:

ThisYear := Ada.Calendar.Year(Date => RightNow);

After executing this function, ThisYear would hold the Year_Number of RightNow.

4. Writing function bodies

·

·

·

· Function Maximum (value1, Value2 : Integer) Return Integer IS

Result : Integer;

BEGIN

IF value1 > Value2 THEN

Result := Value1;

ELSE

Result := value2;

END IF;

RETURN Result;

END Maximum;

5. Using functions in an executable program

· Functions can occur in two places.

· EX. program 5.5 Max_Two

· Function spec before BEGIN and after procedure variable declarations

· Then function body

· Then begin for the executable procedure Max_Two

· Calling the function within the executable procedure

6. Writing a package

· We will often deal with functions that have been encapsulated into reusable packages.

· The spec contains the function declarations

· the package body contain the function bodies