How Ada Programming Language Engaged Modern Millitary Hardwares..

Ada is a structured, statically typed, imperative, wide-spectrum, and object-oriented high-level computer programming language, extended from Pascal and other languages. It has built-in language support for design-by-contract, extremely strong typing, explicit concurrency, tasks, synchronous message passing, protected objects, and non-determinism. Ada improves code safety and maintainability by using the compiler to find errors in favor of runtime errors. Ada is an international standard; the current version (known as Ada 2012^[6]) is defined by ISO/IEC 8652:2012.^[7]

Ada was originally designed by a team led by Jean Ichbiah of CII Honeywell Bull under contract to the United States Department of Defense (DoD) from 1977 to 1983 to supersede over 450 programming languages used by the DoD at that time.^[8] Ada was named after Ada Lovelace (1815–1852), who has been credited with being the first computer programmer.^[9]

Ada was originally targeted at embedded and real-time systems. The Ada 95 revision, designed by S. Tucker Taft of Intermetricsbetween 1992 and 1995, improved support for systems, numerical, financial, and object-oriented programming (OOP).
Features of Ada include: strong typing, modularity mechanisms (packages), run-time checking, parallel processing (tasks, synchronous message passing, protected objects, and nondeterministic select statements), exception handling, and generics. Ada 95 added support for object-oriented programming, including dynamic dispatch.
The syntax of Ada minimizes choices of ways to perform basic operations, and prefers English keywords (such as "or else" and "and then") to symbols (such as "||" and "&&"). Ada uses the basic arithmetical operators "+", "-", "*", and "/", but avoids using other symbols. Code blocks are delimited by words such as "declare", "begin", and "end", where the "end" (in most cases) is followed by the identifier of the block it closes (e.g., if … end if, loop … end loop). In the case of conditional blocks this avoids a dangling else that could pair with the wrong nested if-expression in other languages like C or Java.

Ada is designed for development of very large software systems. Ada packages can be compiled separately. Ada package specifications (the package interface) can also be compiled separately without the implementation to check for consistency. This makes it possible to detect problems early during the design phase, before implementation starts.
 Language Structure.
Ada is an ALGOL-like programming language featuring control structures with reserved words such as if, then, else, while, for, and so on. However, Ada also has many data structuring facilities and other abstractions which were not included in the original ALGOL 60, such as type definitions, records, pointers, enumerations. Such constructs were in part inherited from or inspired by Pascal.

"Hello, world!" in Ada[edit]

A common example of a language's syntax is the Hello world program: (hello.adb)

with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is

begin
  Put_Line ("Hello, world!");
end Hello;


This program can be compiled by using the freely available open source compiler GNAT, by executing


gnatmake hello.adb.



Data types[edit]
Ada's type system is not based on a set of predefined primitive types but allows users to declare their own types. This declaration in turn is not based on the internal representation of the type but on describing the goal which should be achieved. This allows the compiler to determine a suitable memory size for the type, and to check for violations of the type definition at compile time and run time (i.e., range violations, buffer overruns, type consistency, etc.). Ada supports numerical types defined by a range, modulo types, aggregate types (records and arrays), and enumeration types. Access types define a reference to an instance of a specified type; untyped pointers are not permitted. Special types provided by the language are task types and protected types



For example, a date might be represented as:


type Day_type   is range    1 ..   31;
type Month_type is range    1 ..   12;
type Year_type  is range 1800 .. 2100;
type Hours is mod 24;
type Weekday is (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday);

type Date is
   record
     Day   : Day_type;
     Month : Month_type;
     Year  : Year_type;
   end record;
Types can be refined by declaring subtypes:
subtype Working_Hours is Hours range 0 .. 12;          -- at most 12 Hours to work a day


subtype Working_Day is Weekday range Monday .. Friday;   -- Days to work

Work_Load: constant array(Working_Day) of Working_Hours  -- implicit type declaration
   := (Friday => 6, Monday => 4, others => 10);           -- lookup table for working hours with initialization


Types can have modifiers such as limited, abstract, private etc. Private types can only be accessed and limited types can only be modified or copied within the scope of the package that defines them.[26] Ada 95 adds additional features for object-oriented extension of types.


                                                      Control structures[edit]
Ada is a structured programming language, meaning that the flow of control is structured into standard statements. All standard constructs and deep level early exit are supported so the use of the also supported 'go to' commands is seldom needed.



-- while a is not equal to b, loop. while a /= b loop Ada.Text_IO.Put_Line ("Waiting"); end loop; if a > b then Ada.Text_IO.Put_Line ("Condition met"); else Ada.Text_IO.Put_Line ("Condition not met"); end if; for i in 1 .. 10 loop Ada.Text_IO.Put ("Iteration: "); Ada.Text_IO.Put (i); Ada.Text_IO.Put_Line; end loop; loop a := a + 1; exit when a = 10; end loop; case i is.


when 0 => Ada.Text_IO.Put ("zero");
  when 1 => Ada.Text_IO.Put ("one");
  when 2 => Ada.Text_IO.Put ("two");
  -- case statements have to cover all possible cases:
  when others => Ada.Text_IO.Put ("none of the above");
end case;

for aWeekday in Weekday'Range loop               -- loop over an enumeration
   Put_Line ( Weekday'Image(aWeekday) );         -- output string representation of an enumeration
   if aWeekday in Working_Day then               -- check of a subtype of an enumeration
      Put_Line ( " to work for " &
               Working_Hours'Image (Work_Load(aWeekday)) ); -- access into a lookup table
   end if;c
end loop;