Object-oriented Software in Ada 95

4 Introduction to programming
1.5.1 Making the solution more general
The calculation using the pocket calculator can be made more general by storing the price of the apples in the
calculator's memory. The price of a specific amount of apples can then be calculated by retrieving the stored price
of the apples and multiplying this retrieved amount by the quantity required. For example, to setup the price of
apples in the calculator's memory and calculate the cost of 4.1 kilos of apples, the process is as follows:
Pocket calculator Step Steps performed
1 Enter the cost of a kilo of apples:
C 1 . 2 0
S M / *
7 8 9
4.92
-
2
3
Save this value to the calculator’s memory:
S
Retrieve the value from memory:
M
4 5 6 +
1 2 3 C
0 . =
4
5
6
Enter the operation to be performed:
*
Enter the number of kilos to be bought:
4 . 1
Enter calculate
=
To calculate the price for each customer’s order of apples, only steps 3—6 need be repeated. In essence, a
generalized solution to the problem of finding the price of any quantity of apples has been defined and
implemented.
1.6 Solving the problem using the Ada 95 language
To solve the problem of calculating the cost of a quantity of apples using the programming language Ada 95, a
similar process to that used previously when using a pocket calculator is followed. This time, however, the
individual steps are as follows:
Note:
Step Description
1 Set the memory location Price_per_kilo to the cost per kilogram of the
apples.
2 Set the memory location Kilos_of_apples to the kilograms of apples
required.
3 Set the memory location Cost to the result of multiplying the contents of
memory location Price_per_kilo by the contents of the memory location
Kilos_of_apples.
4 Print the contents of the memory location Cost.
Although a shorter sequence of steps can be written to calculate 1.2 multiplied by 5.2 the above
solution can easily be extended to allow the price of any number of kilograms of apples to be
calculated.
In Ada 95 like most programming languages when a memory location is required to store a value, it must first be
declared. This is done for many reasons, some of these reasons are:
• So that the type of items that are to be stored in this memory location can be specified. By
specifying the type of the item that can be stored the compiler can allocate the correct amount
of memory for the item as well as checking that a programmer does not accidentally try and
store an inappropriate item into the memory location.
© M A Smith - May not be reproduced without permission