Object-oriented Software in Ada 95

Introduction to programming 3
they expected. The computer obeys the programming language statements exactly. However, in their formulation
the novice programmer has formulated a solution that does not solve the problem correctly.
1.4 A small problem
A local orchard sells some of its rare variety apples in its local farm shop. However, the farm shop has no electric
power and hence uses a set of scales which just give the weight of the purchased product. A customer buying
apples, fills a bag full of apples and takes the apples to the shop assistant who weighs the apples to determine their
weight in kilograms and then multiples the weight by the price per kilogram.
If the shop assistant is good at mental arithmetic they can perform the calculation in their head, or if mental
arithmetic is not their strong point they can use an alternative means of determining the cost of the apples.
1.5 Solving the problem using a calculator
For example, to solve the very simple problem of calculating the cost of 5.2 kilos of apples at £1.20 a kilo using a
pocket calculator the following 4 steps are performed:
Pocket calculator Step Steps performed
6.24
S M / *
7 8 9 -
4 5 6 +
1
2
3
Enter the cost of a kilo of apples:
C 1 . 2 0
Enter the operation to be performed:
*
Enter the number of kilos to be bought:
5 . 2
1 2 3
0 .
C
=
4
Enter calculate
=
Note: The keys on the calculator are:
C
Clear the display and turn on the calculator if off
S
Save the contents of the display into memory
M
Retrieve the contents of the memory
+ - * / Arithmetic operations
* Multiply / Division
+ plus - minus
= Calculate
When entered, these actions cause the calculation 1.20 * 5.2 to be evaluated and displayed. In solving the
problem, the problem is broken down into several very simple steps. These steps are in the ‘language’ that the
calculator understands. By obeying these simple instructions the calculator ‘solves’ the problem of the cost of 5.2
kilos of apples at £1.20 a kilo.
© M A Smith - May not be reproduced without permission