Ada- attempting to remove blank spaces from a string? - string

Question

This question is in regards to a program I'm working on for an intro to programming class in Ada. The only packages I can use are the basic text, integer, and float packages. I'm writing a procedure right now to remove the spaces from the string and I keep getting a constraint error on the same line. This is the line:
if inputString(count) /= Character'Val(32) then
I have count set to start at 1 and then increment through a loop until the end of the string, which would in turn check each character of the string to see if it was different than the character value of a blank space (32). I was then going to include this line:
noSpace(count..count) := inputString(count..count)
where noSpace is to be the string with no spaces. My line of thinking may be completely off and I may need to approach this from a completely different angle.
Update: I've now managed to get past the error message and successfully remove the spaces from my string. But now when I print the new string there is a random variety of characters and shaded spaces after it. I believe the problem is caused because the new string is shorter than the previous one and the last characters are different.

Answer 1

Probably the bug is hid somewhere else.
Try this:
with Ada.Text_IO;
procedure String_Remove_Space is
function Count_Space( S : String ) return Natural is
Sum_Of_Space : Natural := 0;
begin
for I in S'range loop
if S(I) = ' ' then
Sum_Of_Space := Sum_Of_Space + 1;
end if;
end loop;
return Sum_Of_Space;
end Count_Space;
Input_String : String := "Apple is on the tree";
Input_No : String := "AppleIsOnTheTree";
No_Space : String(1..Input_String'Length - Count_Space(Input_String));
Index : Positive := 1;
begin
for I in Input_String'range loop
if Input_String(I) /= ' ' then
No_Space(Index) := Input_String(I);
Index := Index + 1;
end if;
end loop;
Ada.Text_IO.Put_Line(Input_String);
Ada.Text_IO.Put_Line(No_Space);
end String_Remove_Space;

Answer 2

If there are spaces in your input string, the valid part of the output string must be shorter. I imagine you wrote something like
noSpace : String := inputString;
to start things off with noSpace as long as it would need to be if there were no spaces in inputString? then, as you squeeze the spaces out, you seem to be writing garbage (undefined characters) to the end of noSpace. This doesn’t matter so long as you only deal with the valid part.
I tried this:
with Ada.Text_IO; use Ada.Text_IO;
procedure Lareaper is
function Strip_Space (S : String) return String is
Result : String := S;
Current : Positive := Result'First;
Last : Natural := Result'Last;
begin
loop
exit when Current > Last; -- processed the whole string
if Result (Current) = ' ' then
-- slide the rest of the string back one
Result (Current .. Last - 1) := Result (Current + 1 .. Last);
-- which reduces the length by 1 too
Last := Last - 1;
else
-- non-space character, skip
Current := Current + 1;
end if;
end loop;
-- return only the part of the result that doesn't contain spaces
return Result (Result'First .. Last);
end Strip_Space;
begin
Put_Line ('|' & Strip_Space ("") & '|');
Put_Line ('|' & Strip_Space (" ") & '|');
Put_Line ('|' & Strip_Space ("a") & '|');
Put_Line ('|' & Strip_Space ("ab") & '|');
Put_Line ('|' & Strip_Space (" a") & '|');
Put_Line ('|' & Strip_Space ("a ") & '|');
Put_Line ('|' & Strip_Space ("a b") & '|');
Put_Line ('|' & Strip_Space (" a b ") & '|');
end Lareaper;
which outputs
$ ./lareaper
||
||
|a|
|ab|
|a|
|a|
|ab|
|ab|

Answer 3

Count should start at InputString'First, not at 1.
In particular, when InputString is created as a slice/substring of another string, it is very likely that its first character is not at index 1.

Answer 4

Just to show you another possible solution, although one I would never use in real life:
function Strip_Space (S : String) return String is
begin
if S'Length = 0 then
return "";
elsif S (S'First) = ' ' then
return Strip_Space (S (S'First + 1 .. S'Last));
else
return S (S'First) & Strip_Space (S (S'First + 1 .. S'Last));
end if;
end Strip_Space;
And then there's the way I would really do it. I didn't read Simon's answer carefully enough to realize that he was sliding substrings around. The most efficient answer, I think, is similar to Mark's, but you don't actually need to count the spaces in the string first.
function Strip_Space (Input_String : String) return String is
No_Space : String(1..Input_String'Length);
Index : Positive := 1;
begin
for I in Input_String'range loop
if Input_String(I) /= ' ' then
No_Space(Index) := Input_String(I);
Index := Index + 1;
end if;
end loop;
return No_Space(1 .. Index - 1);
end Strip_Space;