How to retrieve Y/N from user in Ada - input

Question

I wrote a program that will determine whether some imaginary school would have a snow day or not. I have the program working correctly I'm just having an issue.
Basically what I want is for the True/False to be Y/N. And later when I print SnowDay --tells whether there's a snow day. Then it will print either "Yes" or "No" instead of "True" or "False"
SofieAssignment : Boolean;
SnowDay : Boolean;
.
.
Put(Item => "Does Sophie have a big assignment due in class, True/False? ");
Get(Item => SophieAssignment);
.
.
Put(Item => "Should we have a snow day today? " & Boolean'Image (SnowDay));

Answer 1

Assuming I understand what you're trying to do:
(1) If you want the user to enter Y or N for SophieAssignment, there are a couple possibilities:
You can input a string and analyze the string yourself.
Put(Item => "Does Sophie have a big assignment due in class, True/False? ");
declare
Answer : String := Get_Line; -- Get_Line is in Ada.Text_IO
begin
if Answer = "Y" or else Answer = "y" or else Answer = "Yes" or else
Answer = "yes" then
SophieAssignment := True;
elsif Answer = "N" or else Answer = "n" or else Answer = "No" or else
Answer = "no" then
SophieAssignment := False;
else
-- whatever you want to do for an invalid entry
end if;
end;
(This could be improved, but I'm just trying to cover the fundamental approach.) Another possibility is to define your own enumeration that has the values Y and N:
type Yes_No is (N, Y);
package Yes_No_IO is new Enumeration_IO (Yes_No); -- Enumeration_IO is in Ada.Text_IO
Answer : Yes_No;
Put(Item => "Does Sophie have a big assignment due in class, True/False? ");
Yes_No_IO.Get(Item => Answer);
SophieAssignment := (Answer = Y);
Get here will set Answer to either Y or N if the user enters the enumeration name (in either case); it will raise Data_Error if something else is entered. I'd prefer the first method if you want better control over how input is handled. For the second, if the user enters "Y Z", Get will return the Y, and the Z is left in the input stream waiting for the next input operation. Also, the first method allows for multiple possible answers better than the second, although you could make it work with an enumeration like
type Yes_No is (N, No, Y, Yes);
(2) To output "Yes" or "No" based on a Boolean, you can use a function as in Keith's answer, or you can set up an array:
type Const_String_Acc is access constant String;
Yes_No_Image : constant array (Boolean) of Const_String_Acc :=
(False => new String' ("No"),
True => new String' ("Yes"));
Put(Item => "Should we have a snow day today? " & Yes_No_Image (SnowDay).all);

Answer 2

To print a Boolean value as "Yes" or "No", just write a function:
function Boolean_Image(B: Boolean) return String is
begin
if B then
return "Yes";
else
return "No";
end if;
end Boolean_Image;
and use it in place of Boolean'Image.
To read a value from the user as Y or y for True, or as N or n for False, just read a Character value and test it to determine which Boolean value to set. Think about how you want to respond if the character the user enters is not any of Y, y, N, or n. You can use Get_Immediate to read a single character without waiting for a newline on input.

Answer 3

type Snow_Day_Type is new Boolean;
function Yes return Snow_Day_Type is (Snow_Day_Type'(True));
function No return Snow_Day_Type is (Snow_Day_Type'(False));