In pascal, how can I check if real variable is in range?

Question

In any other language it's simple, but in Pascal I still have problems. With integer variables, I want to read from user value between 1 and 12, so I simply do:

Program HelloWorld(output);

{$mode objFPC}

var
    a: integer;

begin
     repeat
        writeln('Provide a, a in [1,12]:');
        readln(a);   
     until (a in [1..12]);    
end.

What if I want to check, if a is in [0,3.14159]? So basically a is real not integer. How to solve something like this?

Answer 1

The in operator in pascal is not checking ranges but sets so

a in [1..12]

does not check if a is in a range of 1..12 but checks whether a is in a set constructed from the Integers from 1..12. This would be quite problematic for Real values.

So the only consistent way would be checking

(a >= 0) and (a <= 3.14159)

Of course you can create a respective function if you want.

function inrange(val, lower, upper: real): boolean;
begin
  inrange := (lower <= val) and (upper >= val);
end;


var a: real;
begin
  repeat
    writeln('Provide a, a in [0, 3.14159]:');
    readln(a);   
  until inrange(a, 0, 3.14159);  
end.