Other Loop forms, Procedures Exception Handling

1
Chapter 7

• Other Loop forms, Procedures Exception Handling

2
The General Loop and Exit

• Problems with FOR statement, when
• The loop does not step through all the values of
  a discrete type in forward or reverse order
• The Loop control variable is not discrete
• The number of iterations depends on conditions
  during the execution of the loop

3
Example - Looping when the increment is NOT 1

• WITH Ada.Text_IO
• WITH Ada.Integer_Text_IO
• PROCEDURE Odd_Numbers IS
• --------------------------------------------------
  ------------
• --------------------------------------------------
  ------------
• OddNumber Integer
• BEGIN -- Odd_Numbers
• OddNumber 1 -- initialize
  loop
• LOOP
• EXIT WHEN OddNumber gt 39 -- test for
  exit
• Ada.Integer_Text_IO.Put(Item gt Oddnumber,
  Width gt 3)
• OddNumber Oddnumber 2 -- update
• END LOOP
• Ada.Text_IO.New_Line
• END Odd_Numbers

4
Example- Looping when increment is not an integer

• WITH Ada.Text_IO
• WITH Ada.Float_Text_IO
• PROCEDURE Temperature_Table IS
• --------------------------------------------------
  ------------
• -- Displays a table of Fahrenheit and
• -- equivalent Celsius temperatures.
• --------------------------------------------------
  ------------
• CStart CONSTANT Float 100.0 -- initial
  Celsius temp
• CStep CONSTANT Float -10.0 -- change in
  Celsius temp
• CLimit CONSTANT Float -20.0 -- final
  Celsius temp
• Celsius Float -- Celsius
  temp
• Fahrenheit Float -- Fahrenheit
  temp

5
Cont. Example

• BEGIN -- Temperature_Table
• Ada.Text_IO.Put(Item gt "Celsius
  Fahrenheit")
• Ada.Text_IO.New_Line (Spacing gt 2)
• Celsius CStart -- initialize
• LOOP
• EXIT WHEN Celsius lt CLimit -- test for
  exit
• Fahrenheit 1.8 Celsius 32.0
• Ada.Float_Text_IO.Put
• (Item gt Celsius, Fore gt 4, Aft gt 0, Exp
  gt 0)
• Ada.Text_IO.Put(Item gt " ")
• Ada.Float_Text_IO.Put
• (Item gt Fahrenheit, Fore gt 3, Aft gt 1,
  Exp gt 0)
• Ada.Text_IO.New_Line
• Celsius Celsius CStep -- update
• END LOOP
• END Temperature_Table

6
LOOP Statement

• LOOP
• statement sequence
• EXIT WHEN condition
• statement sequence
• END LOOP

7
ExampleLooping Controlled by an Event

• WITH Ada.Text_IO
• WITH Ada.Float_Text_IO
• PROCEDURE Worm_and_Apple IS
• --------------------------------------------------
  ------------
• -- Displays distances between a worm and an
  apple. The worm
• -- keeps reducing the distance by its body
  length until it is
• -- close enough to bite the apple.
• --------------------------------------------------
  ------------
• SUBTYPE NonNegFloat IS Float RANGE 0.0 ..
  Float'Last
• WormLength CONSTANT NonNegFloat 8.5
• -- worm body length
  in CM
• InitialDist NonNegFloat -- input - starting
  distance
• -- of worm from
  apple
• Distance NonNegFloat -- output -
  diminishing distance
• -- between worm
  and apple

8
Cont. Example

• BEGIN -- Worm_and_Apple
• Ada.Text_IO.Put (Item gt "Initial distance (CM)
  away from apple gt ")
• Ada.Float_Text_IO.Get(Item gt InitialDist)
• Ada.Text_IO.New_Line
• -- Cut the distance between the worm and the
  apple by
• -- the worm's body length until the worm is
  close enough
• -- to bite the apple

9
Cont. Example

• Distance InitialDist --
  initialize
• LOOP
• EXIT WHEN Distance lt WormLength -- test
  for exit
• Ada.Text_IO.Put(Item gt "The distance is ")
• Ada.Float_Text_IO.Put
• (Item gt Distance, Fore gt 4, Aft gt 2, Exp
  gt 0)
• Ada.Text_IO.New_Line
• Distance Distance - WormLength -- update
• END LOOP

10
Cont. Example

• -- Display final distance before entering the
  apple.
• Ada.Text_IO.New_Line
• Ada.Text_IO.Put (Item gt "Final distance
  between worm and apple is ")
• Ada.Float_Text_IO.Put(Item gt Distance, Fore gt
  4, Aft gt 2, Exp gt 0)
• Ada.Text_IO.New_Line
• Ada.Text_IO.Put(Item gt "The worm bites the
  apple.")
• Ada.Text_IO.New_Line
• END Worm_and_Apple

11

• FOR I IN 1..5 LOOP
• Square i i
• Ada.Integer_Text_IO.Put (Item gt i, Width gt
  1)
• Ada.Integer_Text_IO.Put (Item gt Square,
  Width gt 1)
• Ada.Text_IO.New_Line
• END LOOP
• --------------------------------------------------
  ---------------------------------------
• i1
• LOOP
• EXIT WHEN i gt 5
• Square i i
• Ada.Integer_Text_IO.Put (Item gt i, Width gt
  1)
• Ada.Integer_Text_IO.Put (Item gt Square,
  Width gt 1)
• Ada.Text_IO.New_Line
• ii 1
• END LOOP

12

• In General LOOP
• i is needed to declare as a normal variable
• i 1 ---- initialization required
• i i 1 ---- increment/decrement required
• i gt 7 ----condition to exit required
• In FOR LOOP
• implicit in the FOR LOOP

13
LOOP DESIGN

• Declaration for control variable
• (Initialization) for control variable
• (Increment/decrement) for control variable
• Condition for exit

14
May not need a control variable

• In Some Problems,
• for example,
• Add numbers
• Multiply numbers

15
Flag-Controlled Loop

• Initialize Sun to 0
• Initialize MoreData to Y
• LOOP
• EXIT WHEN MoreData N
• Read the next number to num
• Add num to Sum
• Read the next value of MoreData(Y or N)
• END LOOP

16
Example-Flag-Controlled Loop

• Sum 0
• MoreData Y
• LOOP
• EXIT WHEN MoreData N
• Ada.Text_IO.Put(Item gt Enter the next
  number )
• Ada.Integer_Text_IO.Get (Item gt num)
• Sum Sum num
• Ada.Text_IO.New_Line
• Ada.Text_IO.Put(Item gt Any more data Y
  (Yes) or N (No) )
• Ada.Text_IO.Get( Item gt MoreData)
• END LOOP

17
Sentinel-Control Loops

• Initialize Sum to 0
• Read the first number into num
• Loop
• Exit WHEN num is the sentinel
• Add num to Sum
• Read the next number into num
• END LOOP

18
Example -Sentinel-Control Loops

• Sum 0
• Ada.Text_IO.Put(Item gt When done, enter -1 to
  stop )
• Ada.Text_IO.Put(Item gt Enter the first number
  )
• Ada.Integer_Text_IO.Get (Item gt num)
• Ada.Text_IO.New_Line
• LOOP
• EXIT WHEN Num Sentinel
• Sum Sum num
• Ada.Text_IO.Put(Item gt Enter the next
  number )
• Ada.Integer_Text_IO.Get (Item gt num)
• Ada.Text_IO.New_Line
• END LOOP

19
Sentinel-Controlled Loop with a Priming Read

• Read the first value of input variable
• LOOP
• EXIT WHEN input variable is equal to sentinel
• ----
• ----
• Read the next value of input variable
• END LOOP

20
Example ---To add positive numbers---if
negative number, exit loop

• Sum 0
• LOOP
• Ada.Integer_Text_IO.Get (Item gt num)
• EXIT WHEN num lt0
• Sum Sum num
• END LOOP

21
Example ---To multiply positive numbers---if
negative number, exit loop

• Product 1
• LOOP
• Ada.Integer_Text_IO.Get (Item gt num)
• EXIT WHEN num lt0
• Product Product num
• END LOOP

22
Example ---To add positive numbers---if product
is more than 1000, exit loop

• Product 1
• LOOP
• Ada.Integer_Text_IO.Get (Item gt num)
• EXIT WHEN product gt 1000
• Product Product num
• END LOOP