Object-oriented Software in Ada 95

6 Introduction to programming
An animation of the above Ada 95 program is shown below. In the animation the contents of the memory
locations are shown after each individual Ada 95 statement is executed. When a memory location is declared in
Ada 95 inside a function its initial contents are undefined.
Ada 95 statements price kilos Cost
Price_per_kilo : Float;
U U U
Kilos_of_apples : Float;
Cost : Float;
Price_per_kilo := 1.20;
Kilos_of_apples := 5.2;
Cost := Price_per_kilo *
Kilos_of_apples;
Put( Cost );
Note:
1.20 U U
1.20 5.2 U
1.20 5.2 6.24
1.20 5.2 6.24
U indicates that the contents of the memory location are undefined.
Due to lack of room in the title column the variable Price_per_kilo is represented by price
and Kilos_of_apples by kilos.
1.6.1 Running the program
The above lines of code, though not a complete Ada 95 program, form the core code for such a program. When
this code is augmented with additional peripheral code, compiled and then run, the output produced will be of the
form:
6.24
A person who knows what the program does, will instantly know that this represents the price of 5.2 kilograms
of apples at £1.20 a kilogram. However, this will not be obvious to a casual user of the program.
1.7 The declare block
In Ada a declaration is separated from an executable statement. One way of expressing this split is the declare
block that is specified as follows:
declare
Cost : Float;
begin
Cost := 5.2 * 1.20;
Put( Cost );
end;
Note:
By using this construct our Ada 95 programming statements are almost a complete program.
© M A Smith - May not be reproduced without permission