Object-oriented Software in Ada 95

Introduction to programming 11
Cost := Price_Per_Kilo * Kilos_Of_Apples;
Put( Kilos_Of_Apples );
Put( " " );
Put( Cost );
New_Line;
Kilos_Of_Apples := 0.2;
Cost := Price_Per_Kilo * Kilos_Of_Apples;
Put( Kilos_Of_Apples );
Put( " " );
Put( Cost );
New_Line;
etc.
end;
Whilst this is a feasible solution, if we want to calculate the cost of 100 different weights this will involve
considerable effort and code. Even using copy and paste operations in an editor to lessen the typing effort, will
still involve considerable effort! In addition, the resultant program will be large and consume considerable
resources.
1.13 Introduction to the while statement
In Ada 95 a while statement is used to repeat program statements while a condition holds true. A while
statement can be likened to a rail track as illustrated in Figure 1.2. While the condition is true the flow of control
is along the true track. Each time around the loop the condition is re-evaluated. Then, when the condition is found
to be false, the false track is taken.
Condition
False
True
Statements
Executed while
condition is true
Figure 1.2 The while statement as a rail track.
In a while loop the condition is always tested first. Due to this requirement if the condition initially evaluates
to false then the code associated with the while loop will never be executed.
© M A Smith - May not be reproduced without permission