How to output Integers using the Put_Line method?

Question

I can't get this program to compile because it doesn't seem to print integer variables along with strings in the Put_Line method. I've looked at source code online and it works when they do it so where am I going wrong. Thanks for your help.

with Ada.Text_IO;                       use Ada.Text_IO;
with Ada.Integer_Text_IO;           use Ada.Integer_Text_IO;

procedure MultiplicationTable is

    procedure Print_Multiplication_Table(Number :in Integer; Multiple :in Integer) is
        Result : Integer;   
    begin
        for Count in 1 ..Multiple
        loop
            Result := Number * Count;
            Put_Line(Number & " x " & Count & " = " & Result);
        end loop; 
    end Print_Multiplication_Table;
    Number  :   Integer;
    Multiple    :   Integer;

begin
    Put("Display the multiplication of number: ");
    Get(Number);
    Put("Display Multiplication until number: ");
    Get(Multiple);
    Print_Multiplication_Table(Number,Multiple);
end MultiplicationTable;`

Answer 1

The problem is that you're using & with strings and integers. Try one of the following:

Replace Number inside the parameter of put with Integer'Image(Number)

Or break up the Put_Line into the components that you want; ex:

-- Correction to Put_Line(Number & " x " & Count & " = " & Result);
Put( Number );
Put( " x " );
Put( Count );
Put( " = " );
Put( Result);
New_Line(1);

Answer 2

You're already have with and use clauses for Ada.Integer_Text_IO, but you're not actually using it.

Change this:

Put_Line(Number & " x " & Count & " = " & Result);

to this:

Put(Number); Put(" x "); Put(Count); Put(" = "); Put(Result); New_Line;

(I normally wouldn't put multiple statements on one line, but in this case it makes sense.)

Note that Integer'Image prepends non-negative integers with a space, something I've always found greatly annoying; Ada.Integer_Text_IO.Put doesn't do that (unless you ask it to).

You could define overloaded "&" functions, something like this:

function "&"(Left: String; Right: Integer) return String is
begin
    return Left & Integer'Image(Right);
end "&";

function "&"(Left: Integer; Right: String) return String is
begin
    return Integer'Image(Left) & Right;
end "&";

which would make your original Put_Line call valid, but the multiple Put calls are probably better style.

Answer 3

Try this:

Put_Line(Integer'Image(Number) & " x " & Integer'Image(Count) & " = " & Integer'Image(Result));

Answer 4

Building on the answer (and a comment in another question) from Keith Thompson, here is a full Ada program that can output strings and integers with &, using Put_Line, but without the spaces that Integer'Image would otherwise prepend:

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;

procedure Main is

function lstrip(S: String) return String is
begin
    if S(S'First) = ' ' then
        return S(S'First+1 .. S'Last);
    else
        return S;
    end if;
end;

function "&"(Left: String; Right: Integer) return String is
begin
    return Left & lstrip(Integer'Image(Right));
end "&";

function "&"(Left: Integer; Right: String) return String is
begin
    return lstrip(Integer'Image(Left)) & Right;
end "&";

begin
   Put_Line("x=" & 42);
end Main;