CS101	Computer Programming and Utilization	End Sem
19/11/2003					2.30-5.30

(Answer in the question paper itself. No extra sheet will be given.
You may use rough sheets but do not attach any with the quetion-cum-
answer paper.)

Q1. Read the program below very carefully and fill the statements in the
    places marked ****1****, ****2*** etc. Use the side of the paper
    or the back side or the extra blank sheet provided.

program abc
implicit none

integer,parameter:: lower=0,upper=101, size=20,left=1,right=2
integer,dimension(size)::a
integer:: j,nvals

type:: cell
	integer:: val
	type(cell),pointer:: forward,back
end type

type(cell),target:: first,last !first and last cells
type(cell),pointer::moving

first%val=lower
last%val= upper
first%forward=>last
nullify(first%back)
last%back=>first
nullify(last%forward)

write (*, '("Give the number of numbers to be sorted")')
read *,nvals
write (*, '("Give the numbers (between 1 to 100)")')
read *, (a(j), j=1,nvals)

call read_and_insert
call print_seq

contains

subroutine read_and_insert
integer:: i,v,d
moving=>first
do i=1,nvals
	v=a(i)
	call position(v,d) !return the position and the direction of linking
	call add_elt(d,v)
end do
end subroutine

subroutine print_seq
type(cell),pointer::ptr
write (*, '("Ascending order")')
ptr=>first%forward
do
	write(*,'(i4)',advance='no') ptr%val
	ptr=>ptr%forward
	if (.not.associated(ptr%forward)) exit
end do
write(*,*)
write (*, '("Descending order")')
****1****
end subroutine

subroutine add_elt(direction,val) 
integer,intent(in):: direction,val
type(cell),pointer:: ptr,temp

nullify(ptr)
allocate(ptr)
ptr%val=val
nullify(ptr%forward,ptr%back)

if (direction==left) then 
	****2****
else 
	****3****
end if
end subroutine

subroutine position(vl,dir) !take in the value and return the position 
                            ! and direction of linking
integer,intent(in):: vl
integer,intent(out):: dir
!print *, "in position", " vl=",vl," moving%val=",moving%val
do
if (vl > moving%val) then !move forward
		if (.not. associated(moving%forward)) then
				dir=left
				exit
		else
			****4****
		end if
else !move backward
	****5****
end if
end do
end subroutine
end program

                                         5 X 4 = 20
****1***
ptr=>last%back
do
	write(*,'(i4)',advance='no') ptr%val
	ptr=>ptr%back
	if (.not.associated(ptr%back)) exit
end do

****2***
	temp=>moving%back
        moving%back=>ptr
        temp%front=>ptr
        ptr%back=>temp
        ptr%front=>moving
        moving=>moving%back

****3***
        temp=>moving%front
        moving%front=>ptr
        temp%back=>ptr
        ptr%front=>temp
        ptr%back=>moving
        moving=>moving%front

****4***
			moving=>moving%front
                        if (vl < moving%val) then
                                dir=left
                                exit
                        end if

****5***
	  if (.not. associated(moving%back)) then
                                dir=right
                                exit
                else
                        moving=>moving%back
                        if (vl > moving%val) then
                                dir=right
                                exit
                        end if
                end if

Q2.  Write a generic "reversal subroutine", 'rev(x,y)' where 'x' and 
     'y' can be either character strings or integers. 'y' is the reverse 
     of characters of 'x' in case 'x' is a character string and is 
     the reverse of the digits of 'x' in case 'x' is an integer. 
 
                                                 10
(3 for correct module delaration 3 each for the subroutines rev_i and 
rev_s and 1 for main program)

module generic_rev
implicit none

interface all_purpose_rev
	module procedure rev_i
	module procedure rev_s
end interface

contains

subroutine rev_i(a,b)
integer, intent(in)::a
integer,intent(out)::b
integer:: t
t=a
do
 if (t == 0) exit
 b = 10 * b + mod(t, 10)
 t = t / 10
end do
end subroutine rev_i

subroutine rev_s(s1,s2)
character(len=*),intent(in)::s1
character(len=*),intent(out)::s2
integer:: i,j,leng

leng=len_trim(s1)
do i=1,leng
        j=leng-i+1
        s2(i:i)=s1(j:j)
end do
end subroutine rev_s
end module generic_rev

program test_generic_rev
use generic_rev
implicit none
integer:: p,q
character(len=10)::str1,str2

write(*,'("Give integer p")')
read *, p

write(*,'("Give string str1")')
read *, str1

call all_purpose_rev(p,q)
call all_purpose_rev(str1,str2)

write(*,10) q
write(*,20) str2
10 format("Integer reversal result=",i3)
20 format("String reversal result=",a)
end program

Q3. Answer as directed:

(a) Internal subroutines are preceded by ______________ statement; 
    Subroutines outside the program environment are called ____________
    subroutines. (fill in the blank)              
                                                 2
- contains; external

(b) Interface declarations remove the restrictions of _____________,
    _____________ and ________________ matching of formal and actual
    parameters. (fill in the blank)
                                                 3
- type, number and order

(c) The commands for drawing an 'arrow' and a circle in PGPLOT are
    _____________ and ____________ respectively. (fill in the blank)
                                                 2
- PGARRO, PGCIRC

(d) What does the program fragment do (Num1, Num2 and Num3 are positive
    integers)?
                                                 2
	IF ( Num1 < Num2 ) THEN 
		Num3 = Num1;Num1 = Num2;Num2 = Num3
   	END IF
	DO
		Num3 = MOD( Num1, Num2 )
		IF ( Num3 == 0 ) EXIT
		Num1 = Num2;Num2 = Num3
	END DO

- Computes GCD.

(e) Describe in one line what the output of the following program is?
						3
	program abc 
   	implicit none
   	integer, parameter :: max = 9
   	integer            ::  i, j
	10 format (9(2x,i1,a,i1,a,i2))
	do i = 1, max
   		write(*,10) (i, '*', j, '=', i*j, j = 1, max)
	end do 
	end program

- prints the multiplication table  of '1' to '9'.


(f)  Give in one line the purpose of the intrinsic function 'present'.
                                                 2
- checks in the arguement is present in the called procedure.

(g)  Is the following program correct? What is getting 'dereferenced'
     here?                                       2
		integer:: a
		integer, target:: b,c
		integer, pointer:: p1,p2
                p1=>a; b=5;p2=>b; c=p2 

- No, 'a' does not have the target attribute and so 'p1=>a' is 
wrong. 'p2' is getting dereferenced here.

(h)  Mention the four essential components in the 'activation record'
     of a function or subroutine.
                                                4
- arguements, local variables, return value, return address


                     ----------paper ends-----------