Declaration Blocks

Begin - End

• begin - end is similar to {}


• Any begin-end block can contain other begin-end blocks

 
-- Demonstrates using a begin-end block.
-- The extra block has no purpose in the program.

procedure anywhere1 is
   i: integer := 1;
   j: Integer := i;

begin
   i := 2 * i;

   begin
      j := 3 * j;
      put(j);
      new_line;
   end;

end anywhere1;

• Begin-end blocks are used for


1. Declaration blocks: Like Java declare anywhere


2. Exceptions: Like Java try-catch

Declaration Blocks

 
        -- Demonstrates declaring a variable in a declaration block within a program
        with Ada.Text_IO; use Ada.Text_IO;
        with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;

        procedure anywhere2 is
           i: integer := 1;

        begin
           i := 2 * i;

           declare
              j: Integer := i;
           begin
              j := 3 * j + i;
              put(j);
              new_line;
           end;

           -- put(j);  -- Compile error

        end anywhere2;
  

• Variables in a Declare block hide variables with the same name declared in an enclosing block. Hiding variables is not recommended.

Declare blocks and Dynamic Allocation of Strings

 
        -- Demonstrates declaring a string variable whose size is 
        --  not known until runtime

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

        procedure anywhere3 is
           s: String(1..80);
           len: integer;

        begin
           get_line(s, len);
           put(s'length);
           put(len);
           -- How do we output the string that was input?

           declare
              t: String(1..len) := s(1..len); 
           begin
              put(t);
              put(t'length);
           end;

        end anywhere3;
  

• We will discuss strings more later.