with Ada.Text_IO;
use Ada.Text_IO;

package body HelloWorld is
  type list is array(1..stack_size) of object;
  type ob_stack is
      record
          item : list;
          top : natural := 0;
      end record;
  st : ob_stack;

  procedure push(x : in object) is
  begin
      if st.top = stack_size then
          put_line("stack is full");
      else
          st.top := st.top + 1;
          st.item(st.top) := x;
      end if;
  end push;

  procedure pop(x : out object) is
  begin
      if st.top = 0 then
          put_line("stack is empty");
      else
          x := st.item(st.top);
          st.top := st.top - 1;
      end if;
  end pop;

  function stack_is_empty return boolean is
  begin
      return st.top = 0;
  end stack_is_empty;

  function stack_top return object is
  begin
      if st.top = 0 then
          put_line("stack is empty");
          --return ' ';
      else
          return st.item(st.top);
      end if;
  end stack_top;

  function stackSize return integer is
  begin
     return st.top;
  end stackSize;

  procedure reset_stack is
  begin
      st.top := 0;
  end reset_stack;
end HelloWorld;

Ada online compiler

Write, Run & Share Ada code online using OneCompiler's Ada online compiler for free. It's one of the robust, feature-rich online compilers for Ada language, running the latest Ada version 2012. Getting started with the OneCompiler's Ada editor is easy and fast. The editor shows sample boilerplate code when you choose language as Ada and start coding.

Read inputs from stdin

OneCompiler's Ada online editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample Ada program which takes name as input and prints hello message with your name.

with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
  declare
  name : String := Ada.Text_IO.Get_Line;
  begin
  Ada.Text_IO.Put ("Hello ");
  Ada.Text_IO.Put_Line (name);
	end;
end Hello;

About Ada

Ada is suitable for all development needs and it is extremely good for developing very large applications with built-in features which supports structured, object-oriented, generic, distributed and concurrent programming directly. Ada was designed by Jean Ichbiah.

It's a Good choice for Rapid Application Development, Extreme Programming. It is a very strong and statically typed language.

Syntax help

Loops

1. Infinite loop:

This is the simplest loop

begin
   Index := 1; --initialization
    loop                            
     --code
	exit when Index = n;
	end loop;

2. while loop

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

   Count := 1;    --initialization
   while Count < n loop  
   --code
   end loop;

3. for loop

For loop is used to iterate a set of statements based on a condition. Usually for loop is preferred when number of iterations are known in advance.

for Index in 1..n loop          
--code
end loop;

Sub programs

Ada distinguishes functions and procedures. In simpler terms, functions return some value and must be called as part of larger expressions. Procedures never return a value.

Functions and procedures are collectively called as sub-programs.

Syntax for procedure

procedure proc-name
(X : in Integer ; Y : out Integer ; Z : in out Integer ) is
begin
X := 10; −− it's an Error as you can’t modify an in parameter.
Y := X; −− can modify Y as it's an out parameter.
Z := Z + 1; −− can read and write as it's an in out parameter.
end proc-name;

Syntax for functions

function function_name(declaration) return value is
begin
--code
end function-name;