Validating an input in Pascal (pre release material) - delphi

Question

I'm playing around with the comp 1 pre release material, but I can't seem to asnwer this properly in Pascal compiling in delphi...
This question refers to the function RollBowlDie.
This function has no validation of the input value.
What you have to do....
Make a copy of the Skeleton Program. Add additional statements to the function RollBowlDie so that it ensures that the input BowlDieResult is in the range 1 to 6 before allowing the game to continue and outputs an error message if not.
Add further statements to the function RollBowlDie so that it also checks that the input
BowlDieResult does not cause the program to crash if it is the wrong data type and instead outputs an error message when this is detected.
Test the amended function to show that it does not allow inputs that are out of range.
Test the amended function to show that it does not crash if an incorrect data type is added.
This is the RollBowlDie function.
Function RollBowlDie(VirtualDiceGame : Boolean) : Integer;
Var
BowlDieResult : Integer;
Begin
If VirtualDiceGame
Then BowlDieResult := Random(6) + 1
Else
Begin
Writeln('Please roll the bowling die and then enter your result.');
Writeln;
Writeln('Enter 1 if the result is a 1');
Writeln('Enter 2 if the result is a 2');
Writeln('Enter 3 if the result is a 4');
Writeln('Enter 4 if the result is a 6');
Writeln('Enter 5 if the result is a 0');
Writeln('Enter 6 if the result is OUT');
Writeln;
Write('Result: ');
Readln(BowlDieResult);
Writeln;
End;
RollBowlDie := BowlDieResult;
End;
I have tried putting this in, but the message error message didnt come up, and the program crashed when trying in a letter.
Function RollBowlDie(VirtualDiceGame : Boolean) : Integer;
Var
BowlDieResult : Integer;
Begin
If VirtualDiceGame
Then BowlDieResult := Random(6) + 1
Else
Begin
Repeat
Writeln('Please roll the bowling die and then enter your result.');
Writeln;
Writeln('Enter 1 if the result is a 1');
Writeln('Enter 2 if the result is a 2');
Writeln('Enter 3 if the result is a 4');
Writeln('Enter 4 if the result is a 6');
Writeln('Enter 5 if the result is a 0');
Writeln('Enter 6 if the result is OUT');
Writeln;
Write('Result: ');
Try
Readln(BowlDieResult)
Except
Writeln('Not a valid number')
End;
Writeln;
Until (BowlDieResult >= 1) and (BowlDieResult <= 6);
End;
RollBowlDie := BowlDieResult;
End;
I's not sure how to solve the question, any help would be appreciated greatly!

Answer 1

Probably you need to read a string or a char-typed variable instead of an integer one, and then convert the string/char to integer in an controlled way.

Answer 2

Of course it crashes if you type in a letter ... you're specifically asking to
read an integer, and a letter isn't an integer.
Before commenting more on that issue, why not just say:
writeln ('Please enter the number rolled, or 0 if it is an OUT: ');
rather than having 6 writelns? Also, what if a 3 or 5 was rolled (you're only
giving (somewhat odd) directions for the values 1, 2, 4, 6, and 0 ... leaving
out 3 and 5. Keep in mind that you can't get a 0 from "BowlDieResult := Random(6) + 1".
How do you intend the user to indicate "stop" if you're looping until you have
a value between 1 and 6?
Back to the "how do I read a letter" question...
Use a variable of type "char" (or "packed array of char") to read arbitrary text ...
then, compare the character read to '1', '2', ..., '6', or (say) 'Q' (for Quit).
E.g.:
var
answer : char;
attempts : integer; {prevent infinite loop}
done : boolean;
attempts := 0;
saw_quit := false;
done := false; {loop until we get a good number or a QUIT command}
{Or until 9 attempts have been made to enter a #. }
while not done do
begin
writeln ('Please enter a number (1..6) or Q to quit: ');
readln (answer);
if answer in ['1'..'6'] then
begin {we got a number in range 1..6...}
BowlDieResult := ord (answer) - ord ('0'); {convert char to int}
done := true;
end
else if answer in ['Q', 'q'] then {upper or lower case :) }
begin
saw_quit := true;
done := true;
end
else
begin
writeln ('Sorry, that is not a number from 1 to 6 or a "Q"!');
attempts := attempts + 1;
if attempts > 9 then
begin
writeln ('Sorry, too many mistakes ... assuming QUIT');
saw_quit := true;
done := true;
end;
end;
end; {while not done}
Note: the above not tested for compilation ... I NEVER use Pascal's built-in I/O,
for performance and reliability reasons, so I'm rusty with it.
Note: see http://www.allegro.com/papers/htpp.html
for some philosophy of Pascal programming.
Stan