How to have multiple conditionals in an if statement in Ada - if-statement

Question

How would I go about having multiple conditionals in an if statement?
Eg. The user is asked a set of questions by the program:
1.) Enter an altitude between 0 and 1000
(user types in data)
2.) Enter Velocity between 0 and 500
(user types in data)
3.) Enter Temperature between 0 and 200
(user types in data)
the program then prints back
altitude = user value
velocity = user value
temperature = user value //ignore those list numbers
I have set in my (.ads) file that each of these ranges has a criticle value.
I want to create an if statement that has multiple conditionals.
in pseudo : If velocity = critical velocity & temperature = critical temperature & altitude = critical altitude
then print ("some message")
else do nothing

Answer 1

The syntax of an if-statement is
if_statement ::=
if condition then
sequence_of_statements
{elsif condition then
sequence_of_statements}
[else
sequence_of_statements]
end if;
and the syntax of “condition” is
condition ::= boolean_expression
(that is, an expression which happens to be boolean); the syntax of “expression” is
expression ::=
relation {and relation} | relation {and then relation}
| relation {or relation} | relation {or else relation}
| relation {xor relation}
so your code would look like
if velocity = critical_velocity
and temperature = critical_temperature
and altitude = critical_altitude
then
print ("some message”);
else
null;
end if;
You can leave out the else clause, and you can say and then instead of plain and if for some reason you shouldn’t check the rest of the condition if the first part is already False. This is called short-circuit evaluation, and it’s not the default in Ada (it is in C).
if X /= 0 and Y / X > 2 then
evaluates Y / X even if X is 0.

Answer 2

In Ada you will use the and, or and not boolean operator:
if Velocity = Critical_Velocity
and Temperature = Critical_Temperature
and Altitude = Critical_Altitude
then
Ada.Text_IO.Put_Line ("Crash");
else
...
end if;
When evaluation order matters, you will use the and then or the or else syntax (otherwise the compiler can change order for optimization).
Expressions will be evaluated in the 'and then'/'or else' order.
if Velocity = Critical_Velocity
and then Temperature = Critical_Temperature
and then Altitude = Critical_Altitude
then
Ada.Text_IO.Put_Line ("Crash");
else
...
end if;
With an or else, you may write as follows:
if Velocity = Critical_Velocity
or else Temperature = Critical_Temperature
or else Altitude = Critical_Altitude
then
Ada.Text_IO.Put_Line ("Crash");
else
...
end if;
Beware that you cannot mix and and or together (because this leads to many confusion for developers).
You have to use parenthesis arround them if you do it.
if (Velocity = Critical_Velocity and Temperature = Critical_Temperature)
or else Altitude = Critical_Altitude
then
Ada.Text_IO.Put_Line ("Crash");
else
...
end if;