Declarations, Integers, Naturals, Attributes, I/O, Operators

Declarations, Integers, Integer Output

Declare and Print Some Integers

• File some_ints.adb

   with Ada.Text_IO; use Ada.Text_IO;
   with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
      -- Integer I/O library

   procedure some_ints is
      i, j: Integer;
      k: Integer := 333;
      c: constant Integer := 4444;
   begin
      i := 1;
      j := 22;
      put(i); new_line;     -- Default minimum width 12
      put(j); new_line;     -- Default minimum width 12
      put(k, 5);  new_line; -- Minimum width 5
      put(c, 1);  new_line; -- Minimum width 1
   end some_ints;
   --|           1
   --|          22
   --|  333
   --|4444
   

• Integer IO library
• Declaration section
• variable: type
• := for assignment (= is for equality)
• constant
• default width 12
• minimum width
• no put_line for integers

Attributes, Subtypes Natural and Positive

Attributes 'img and 'image

• File some_ints.adb

   with Ada.Text_IO; use Ada.Text_IO;
   procedure images is
      i: Integer := 11;
      j: Integer := -22;
   begin
      put_line(i'img); 
      put_line(j'img); 

      put_line(i'image); 
      put_line(j'image); 

      put_line(Integer'image(i)); 
      put_line(Integer'image(j)); 
   end images;
   --| 11
   --|-22
   --| 11
   --|-22
   --| 11
   --|-22
   

• 'img and 'image - like to_string - convert integer to String
• var'img and var'image - not yet standard


• 'img and 'image are attributes


• 'img and 'image not allowed for structured types (eg arrays)
• Ada 2020 extends 'image for (almost) all types


• More recent versions of Ada allow i'image

More Attributes: 'value, 'first, 'last, 'size

• Variables and types have attributes
• Type attribute: Integer'image(i)
• Variable attribute: i'img;

   with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
   procedure attributes is
      i: Integer := Integer'value("999"); 
   begin
      put(i);              -- 999

      put(Integer'first);  -- smallest Integer
      put(Integer'last);   -- largest  Integer

      put(i'size);         -- 32 (32 bit integers)
   end attributes;
   

• What is the inverse of 'value?

(Sub)Types Natural and Positive

• Use Subtypes Natural and Positive if possible
• Benefit: Catch errors earlier

   with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
   procedure nat_pos is
      Number_Of_Students: Natural := 0;
      Year: Positive := 2017;
   begin
      put(Natural'first); -- What is this?
      put(Natural'last);  -- What is this?

      Number_Of_Students := Number_Of_Students - 1;
      -- Meant to write + 1
   end nat_pos;
   

• Later we learn that Natural and Positive are subtypes of Integers
• Subtype = subset of values, same operations
• Thus, Integers, Naturals, Positives can be mixed freely:

   stupid: Integer := Number_Of_Students;
   weird: Positive := Number_Of_Students + Year;
   weirder: Natural := Number_Of_Students - Year;
   ...
   Ada.Integer_Text_IO.put(Year);
   

Another Attributes: 'range

• Another attributes: 'range

   procedure nat_pos is
      i: Integer;
      Number_Of_Students: Natural := 0;
      Year: Positive := 2017;
   begin
      ...
      if i in Natural'first .. Natural'last then ...

      if i in Positive'range then ...
      -- Positive'range is Positive'first .. Positive'last
      
      for j in My_Array'range loop ...
   end attributes;
   

• 'range is VERY useful for arrays and loops!

Expressions and Operators

Expressions and Operators

• Operators - high to low precedence
1. **, not, abs
2. *, /, mod, rem
3. +, - (unary)
4. +, -, &
5. =, /=, < <=; > >=
6. and, or, xor


• Membership test and short circuit:
1. in - Membership test
2. and then, or else (short circuit)


• Notes:
• words: not, abs, mod, rem, and, or, xor
• Exponentiation: 2 ** 3 = 8, 2 ** -3 = 0.125 = ¹⁄₈
• Absolute value: (eg abs )
• Integer division: (eg 9 / 2 = 4)
• Mod and rem differ only for negative operands
• Clock arithmetic:(2 - 4) mod 12 = 10. (2 - 4) % 12 == -2.
• & is string concatenation: put_line("Hi " & "Mom!");
• put_line("Hi " & "Mom!");
• put_line("x = " & x'img);
• /=
• xor - one or the other but not both
• and, or, xor all at same level
• Parens required if mixed: x = y and (a = b or c = d);
• Membership test (if x in Natural then)
• Short circuit example: if y /= 0 and then x / y > z then
• Only evaluate second operand if needed
• Java??

Integer Input - Different from Java!

Integer Input!

• Similar to - but different - from Scanner s = new Scanner(System.in); i = s.nextInt();

   with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
   procedure get_int is
      i, j, sum: Integer;
   begin
      get(i);
      get(j);
      sum := i + j;
      put(sum);
   end get_int;
   

• Get(i) modifies the value of i
• Get(i) skips white space until it finds an integer