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  <LI> Constraint checking is at run time.
  <LI> Violation raises <code>constraint</code> <em> exception</em>.<BR> 
     (Program is <b> not</b> illegal.)
 </H4>
 </UL></UL>
<P>

<P>
---Slide 12---<BR>
<em> Examples</em>
<P>
<P>
<P>
<H5> <PRE>  subtype NATURAL is INTEGER range 1..INTEGER'LAST;
  A: INTEGER;
  B: FLOAT;
  C: NATURAL;
  D: INTEGER range 0..INTEGER'LAST;

  A := B;              --illegal
  A := INTEGER(B);     --type conversion, legal
  A := C;              --legal
  A := D - 3;          --legal
  A := C + INTEGER(B); --legal
  C := D;              --constraint exception
  C := A;              --constraint exception
</PRE>
</H5>
<P>

<P>
---Slide 13---<BR>
<em> Arrays</em>
<P>
<P>
<P>
<UL><LI> <b> Arrays in Ada:</b>
 <UL><H4>
  <LI> Fixed Size---Type may be <em> unconstrained</em> at definition
But bounds must be given at object declaration.
  <LI> Elements are all of same <em> subtype</em>
  <LI> Permits: Assignment, Equality Testing, Slicing, <!WA7><IMG  ALIGN=BOTTOM ALT="" SRC="http://cs.nyu.edu/cs/dept_info/course_home_pages/fall96/G221.2110/PL/L5/img8.gif">
 </H4>
 </UL>
<H5> <PRE>subtype NATURAL is INTEGER range 1..INTEGER'LAST;
type SHORT_STRING is array(1..10) of CHARACTER;

type STRING is
     array (NATURAL range &lt;&gt;) of CHARACTER;

NAME: STRING(1..10);
</PRE>
</H5></UL>
<P>

---Slide 14---<BR>
<em> Array Assignment</em>
<P>
<P>
<P>
<UL><LI> Assigning array <code>B</code> to <code>A</code>: <tt> A := B</tt>
<H4> <OL><LI> Legal, if type of <code>A</code> is same as type of <code>B</code>.
<P>
 <LI> If <code>A</code> has same number of elements as <code>B</code>, then
<code>B</code> is copied into <code>A</code> <em> positionally</em>---Otherwise, <tt>
constraint-error exception</tt> is raised.
 </OL></H4>
<P>
<H5> <PRE>declare
  A: STRING(1..10); B: STRING(11..20);
begin
  A := B;
end;
</PRE>
</H5>
<P>
<LI> <b> Array Attributes</b><BR> 
<H4>
<P><!WA8><IMG  ALIGN=BOTTOM ALT="" SRC="http://cs.nyu.edu/cs/dept_info/course_home_pages/fall96/G221.2110/PL/L5/img9.gif"><P>
</H4>
</UL>
<P>

---Slide 15---<BR>
<em> Array Indexing &amp; Slicing</em>
<P>
<P>
<P>
<UL><LI> Array Indexing:
<H5> <PRE> S: STRING(1..10);
 S(3) := S(2);
</PRE>
</H5>
<P>
 <LI> Array Slicing (1D arrays only)
<H5> <PRE> S(3..7)              --an array object
 S(3..7) := S(4..8);
 S := S(2..10) &amp; S(1) -- &amp; == concatenation opn
</PRE>
</H5>
<P>
 <LI> Array Aggregates:
<H5> <PRE> type SYM_TAB is array (CHARACTER range &lt;&gt;) of INTEGER;
 TABLE: SYM_TAB('a'..'c') := (0, 1, 2);
 TABLE := ('c' =&gt; 2, 'b' =&gt; 1, 'a' =&gt; 0);
 TABLE := ('c' | 'b' =&gt; 1, others =&gt; 0);
</PRE>
</H5></UL>
<P>

---Slide 16---<BR>
<em> Records</em>
<P>
<P>
<P>
<UL><LI> <b> Records in Ada:</b>
 <UL><H4>
  <LI> <em> Heterogeneous</em>: Components need not be of same type.
  <LI> Fields are accessed by component names: E.g.,
<code>MY_CAR.CAR_MAKE</code>
  <LI> <em> Variant Records</em> Tag (discriminant) fields cannot be
changed at run-time.
  <LI> Permits: Assignment and Equality Testing.
 </H4>
 </UL>
<H5> <PRE> type CAR_MAKE is (FORD, GM, HONDA);
 subtype CAR_YEAR is INTEGER range 1900..1999;
 type CAR is
   MAKE: CAR_MAKE;
   YEAR: CAR_YEAR;
 end record;

 MY_CAR: CAR;
</PRE>
</H5></UL>
<P>

---Slide 17---<BR>
<em> Records (Contd)</em>
<P>
<P>
<P>
<UL><H4>
<LI> Records may be <em> nested</em>...<em> initialized</em> at
declaration.
 <LI> A record <code>B</code> may be assigned to record <code>A</code>, provided
they have same type.
<H5> <PRE>  A, B: CAR;
  A := B;
</PRE>
</H5>
<P>
 <LI> Record Aggregates:
</H4>
<H5> <PRE>  YOUR_CAR: CAR :=           YOUR_CAR: CAR :=
     (GM, 1981);                (MAKE =&gt; GM,
                                 YEAR =&gt; 1981);
</PRE>
</H5></UL>
<P>

---Slide 18---<BR>
<em> Variant Records</em>
<P>
<P>
<P>
<UL><H4>
<LI> Similar to PASCAL variant records:
 <LI> Except---Type declaration only defines a template; When object
is declared, <em> discriminant value must be supplied</em>.
<PRE>     type VEHICLE_TAG is (CAR, TRUCK);
     type VEHICLE(TAG: VEHICLE_TAG) is record
       YEAR: MODEL_YEAR := 93;
       case TAG is
         when CAR =&gt; COLORS: COLOR_SCHEME;
         when TRUCK =&gt; AXLES: NATURAL;
       end case;
     end record;

     YOUR_TRUCK: VEHICLE(TRUCK);
     REFRIGERATOR: VEHICLE;      --Illegal
</PRE>
<P>
 <LI> There may be more than one discriminant...But they must all be
of discrete types....Discriminant can be used as an uninitialized
constraint.
<PRE>     type BUFFER(LENGTH: NATURAL) is record
       POOL: STRING(1..LENGTH);
     end record;
</PRE>
<P>
</H4>
</UL>
<P>

---Slide 19---<BR>
<em> Access Types</em>
<P>
<P>
<P>
<UL><H4>
 <LI> Allow manipulation of pointers.
 <LI> Allow control of object creation.
</H4>
<H5> <PRE>  type STRING_PTR is access STRING;
  type STRING_10_PTR is access STRING(1..10);
  P, Q: STRING_PTR; P10: STRING_10_PTR;

  P10 := new STRING(1..10);
  P10 := new STRING(2..11);    --Constraint Error
  P10 := new STRING;           --Illegal

  P := new STRING(1..3);       --OK
  P.all := &quot;BUD&quot;;
  Q := new STRING(&quot;MUD&quot;);
  P := Q;
  P.all := Q.all
</PRE>
</H5>
<H4>
 <LI> <code>new</code> creates a new object that can be designated by the
access type.
</H4>
<P>
</UL>
<P>

---Slide 20---<BR>
<em> Recursive Types</em>
<P>
<P>
<P>
<PRE>  type NODE;  --Incomplete Declaration;
  type NODE_PTR is access NODE;

  type NODE is
    record
      DATUM: CHARACTER;
      NEXT: NODE_PTR;
    end record;
</PRE>
<P>

---Slide 21---<BR>
<em> Generalized Access Types</em>
<P>
<P>
<P>
<UL><H4>
 <LI> Inherent Access to declared objects<BR> 
	(Not just objects created by allocators)
</H4>
<H5> <PRE>  type INT_PTR is access all INTEGER;

  IP: INT_PTR;
  I: aliased INTEGER;
  IP := I'Access
</PRE>
</H5>
<H4>
 <LI> <b> Note:</b> Designated variable must be marked <code>aliased</code>.
 <LI> <code>Access</code> attribute is only applicable to an object whose
	lifetime is at least that of the access type.
 <LI> Avoids ``dangling reference'' problem.
</H4>
<H5> <PRE>  type CONST_INT_PTR is access constant INTEGER;

  CIP: CONST_INT_PTR;
  C: aliased constant INTEGER := 1815;
  CIP := C'Access
</PRE>
</H5>
<H4>
 <LI> Access is restricted to read-only
</H4>
<P>
</UL>
<P>

<P>
---Slide 22---<BR>
<em> Control Structures</em>
<P>
<P>
<P>
<UL><LI> Assignment Statements
<H5> <PRE>     DISCRIM := (B**2 - 4.0*A*C);
     TABLE(J) := TABLE(J) + 1;
     VECTOR := (1..10 =&gt; 0);
</PRE>
</H5>
<P>
 <LI> Conditional Statements
<H5> <PRE>   if (A=1) then
     ...
   end if;                    case A is
                                when 1 =&gt; --...;
   if (A=1) then                when 2 =&gt; --...;
     --...                      when others =&gt; null;
   elsif (A=2) then           end case;
     --...
   else
     --...
   end if;
</PRE>
</H5></UL>
<P>

---Slide 23---<BR>
<em> Control Structures: Iteration Clause</em>
<P>
<P>
<P>
<UL><LI> Iteration Statements---Basic Loop
<H5> <PRE>  loop
    -- Statements to be repeated
  end loop;
</PRE>
</H5>
<P>
 <LI> <em> Iteration Clause</em><BR> 
<H4>
	Execution of a basic <code>loop</code> terminates when
 <OL><LI> <em> The iteration is completed</em> or
   <LI> <em> A <tt> loop exit</tt> statement is executed</em>
 </OL>
</H4>
<P>
<H5> <PRE>SUM := 0;                SUM := 0;
for I in 1..10 loop      for I in reverse 1..10 loop
 SUM := SUM + A(I);        SUM := SUM + A(I);
end loop;                end loop;

SUM := 0; I := 1;        SUM := 0; I := 1;
while I &lt;= 10 loop       loop
  SUM := SUM + A(I);       exit when I &gt; 10;
  I := I + 1;              SUM := SUM + A(I);
end loop;                  I := I + 1;
                         end loop;
</PRE>
</H5></UL>
<P>

---Last Slide---<BR>
<em> A Complete Ada Program</em>
<P>
<P>
<P>
<H5> <PRE>  with I_O_PACKAGE;
  procedure TEMPERATURE_CONVERSION is
    use I_O_PACKAGE;
    -- Convert temp in Fahrenheit to Celsius

    FAHRENHEIT_TEMP; CELSIUS_TEMP: FLOAT;
  begin
    GET(FAHRENHEIT_TEMP);
    CELSIUS_TEMP := (FAHRENHEIT_TEMP - 32.0)*5.0/9.0;
    PUT(CELSIUS_TEMP);
  end TEMPERATURE_CONVERSION;
</PRE>
</H5>
<P>
[End of Lecture #5]
<P>
</H3>
<P>
<BR> <HR>
<P><ADDRESS>
<I>Bud Mishra <BR>
Thursday October 10 1996</I>
</ADDRESS>
</BODY>