Object-oriented Software in Ada 95

28 Ada introduction: Part 1
3.5 Repetition: while
while Count > 0 loop --loop while greater than 0
-- Repeated statements
end loop;
The above construct repeatedly executes the statements between loop and end loop while the condition
count > 0 is true.
Note:
The mandatory end loop terminates the while loop. In Ada, most constructs are terminated by
a mandatory termination keyword(s). This prevents the kind of errors that can occur in other
languages when an extra statement is added in the belief that it forms part of the construct. It also
allows the compiler to check that the user has constructed a program correctly by matching the start
and end of each construct.
3.6 Selection: if
if Count = 3 then
Put("Ignition"); New_Line;
end if;
--If 3 print Ignition
The if statement allows a statement or statements to be executed only if the condition is true. In the above
example, the statements Put("Ignition"); New_Line; will only be executed when count is equal to 3.
Note:
The mandatory end if terminates the if statement.
An else part may also be included, in which case statement or statements which follow it are only obeyed if
the condition is false. For example:
if Count = 3 then
Put("Count is 3"); New_Line;
else
Put("Count is not 3"); New_Line;
end if;
Note:
The else part of an if statement is optional. However, if it is included it must be followed by at least
one statement.
The rather inelegant nested if structure below:
if Count = 3 then
Put("Count is 3"); New_Line;
else
if Count = 4 then
Put("Count is 4"); New_Line;
else
Put("Count is not 3 or 4"); New_Line;
end if;
end if;
© M A Smith - May not be reproduced without permission