Ada Generic Averaging Function - ada

Question

I have a function which averages a certain numeric value from an array of records. This value is either a natural or an enumerated type delta. I have it summing up the values correctly but my question is this: how do I get the length of an array into a generic type, so that it can divide both integers and delta type numbers?

Answer 1

On your array-of-records use the 'Length attribute; this has the advantage of always working even if your bounds are somewhat odd, like -18..3, or an enumeration, like cheeses..fruits.
Something like:
Function Average( Input : In Array_of_Records ) Return float is
-- You say you already have a summation function, so...
Sum : Natural:= Summation( Input );
Begin
Return Sum / Input'Length;
End Average;
You may need to convert the numeric types, by saying Float(Sum) or the like, as Ada does no automatic type "promotions."

Answer 2

This has some flaws in it, but is this closer to what you wanted ?
NWS.
with Ada.Text_Io;
procedure Main is
generic
type Element_T is private;
Zero : Element_T;
One : Element_T;
type Vec_T is array (Integer range <>) of Element_T;
with function "+"(Left, Right : in Element_T) return Element_T is <>;
with function "/"(Left, Right : in Element_T) return Element_T is <>;
package Arrayops is
function Sum (Vec : in Vec_T) return Element_T;
function Count (Vec : in Vec_T) return Element_T;
function Average (Vec : in Vec_T) return Element_T;
end Arrayops;
package body Arrayops is
function Sum (Vec : in Vec_T) return Element_T is
S : Element_T := Zero;
begin
for I in Vec'First .. Vec'Last loop
S := S + Vec(I);
end loop;
return S;
end Sum;
function Count (Vec : in Vec_T) return Element_T is
C : Element_T := Zero;
begin
for I in Vec'First .. Vec'Last loop
C := C + One;
end loop;
return C;
end Count;
function Average (Vec : in Vec_T) return Element_T is
S : constant Element_T := Sum (Vec);
Len : constant Element_T := Count (Vec);
begin
return S / Len;
end Average;
end Arrayops;
type Fl_Arr_T is array (Integer range <>) of Float;
package Fl_Arr is new Arrayops (Element_T => Float,
Zero => 0.0,
One => 1.0,
Vec_T => Fl_Arr_T);
type Int_Arr_T is array (Integer range <>) of Integer;
package Int_Arr is new Arrayops (Element_T => Integer,
Zero => 0,
One => 1,
Vec_T => Int_Arr_T);
My_Ints : constant Int_Arr_T (1 .. 5) := (6,7,5,1,2);
My_Floats : constant Fl_Arr_T (1 .. 7) := (6.1,7.2,5.3,1.4,2.5,8.7,9.7);
Int_Sum : constant Integer := Int_Arr.Sum (My_Ints);
Int_Count : constant Integer := Int_Arr.Count (My_Ints);
Int_Avg : constant Integer := Int_Arr.Average (My_Ints);
Float_Sum : constant Float := Fl_Arr.Sum (My_Floats);
Float_Count : constant Float := Fl_Arr.Count (My_Floats);
Float_Avg : constant Float := Fl_Arr.Average (My_Floats);
begin
Ada.Text_Io.Put_Line ("Integers => Sum: " & Integer'Image (Int_Sum) & ", Count: " & Integer'Image (Int_Count) & ", Avg: " & Integer'Image (Int_Avg));
Ada.Text_Io.Put_Line ("Floats => Sum: " & Float'Image (Float_Sum) & ", Count: " & Float'Image (Float_Count) & ", Avg: " & Float'Image (Float_Avg));
end Main;
Result :
Integers => Sum: 21, Count: 5, Avg: 4
Floats => Sum: 4.09000E+01, Count: 7.00000E+00, Avg: 5.84286E+00

Answer 3

Expanding on Shark8 a bit here...
Ada allows you to declare array types as unconstrained. Something like
type Array_of_Records is array (Natural range <>) of My_Record;
Gives you a type that can be used for arrays of records with starting and ending array indices that could be anywhere in the range of Natural.
One of the nifty things I can do with such a type is use it as a subroutine parameter, like so:
function Sum (Vector : in Array_of_Records) return Natural;
OK, so inside that routine, how do I know where the array bounds are? By using attributes, like so:
for index in Vector'first..Vector'last loop
or
for index in Vector'range loop
Of course for this to work, you must pass in a perfectly-sized array to your Sum routine. Supppose that isn't what you have. Suppose you instead have a huge array (kind of a buffer) and not all of the values are valid? Well, you keep track of what are the valid values, and pass in only those by using a slice.
Rec_Buffer : Array_of_Records (1..10_000);
Last_Valid_Rec : Natural := 0;
....
--// Rec_Buffer gets loaded with 2,128 values or something. We pass it into Sum
--// like so:
Ada.Text_IO ("Sum of vector is " &
natural'image(Sum (Rec_Buffer (1..Last_Valid_Rec));
(warning - uncompiled code)