Download end do

Repeating
parts of your
program
1
Repeating parts of your program
A very large proportion of mathematical techniques rely on
some form of iterative process, while the processing of most
types of data requires the same or similar actions to be
carried out repeatedly for each set of data. One of the most
important of all programming concepts, therefore, is the ability
to repeat sequences of statements, either a predetermined
number of times or until some condition is satisfied.
F has a very powerful, simple to use, facility for controlling
the repetition of blocks of code.
The use of repetitive techniques, however, often leads to
situations in which it is requested to end the repetition earlier
than had been anticipated.
2
Repeating parts of your program
A “repetitive structure” or “loop” makes possible
the repeated execution of one or more statements
called “body of the loop”.
There are two basic types of repetition :
 “repetition controlled by a counter” , in which
the body of the loop is executed once for each
value of some control variable in a specified range
of values.
 “repetition controlled by a logical expression”,
in which the decision to continue or to terminate
the repetition, is determined by the value of some
logical expression.
3
Program
repetition
• In many cases, we have to repeat
certain sections of a program
• Many numerical methods involve
repetition/iteration
• We have to have construct to repeat
a group of statements, to end the
repetition, or to restart it when
certain condition is fulfilled.
4
Consider this program – Average of 6
numbers
real x1, x2, x3, x4, x5, x6
real sum, avg
read*, x1
read*, x2
read*, x3
read*, x4
read*, x5
read*, x6
sum = x1 + x2 + x3 + x4 + x5 + x6
avg = sum / 6.0
print*, avg
end
Using DO loop
real x
real sum, avg
sum = 0
do k = 1, 6
read*, x
sum = sum + x
contınue
avg = sum / 6.0
prınt*, avg
end
EXAMPLE for a TYPICAL CYCLE :
Repeat the following 3 steps 21 times considering 5oC
intervals from 0oC till to 100oC without the need for any
data to be read at all :
1.step : read the initial and last Celcius temperature
2.step : calculate the corresponding Fahrenheit
temperature for 5oC intervals
3.step : print both tempratures
A sequence of statements which are repeated is called a
“loop.“
The do – constructs provides the means for controlling the
repetition of statements within a loop.
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DO LOOP – TYPE 1
In this count-controlled do loop, the do variable is
incremented by the unit value “1” on each pass starting
from the initial_value (inclusive) till to the final_value
(inclusive).
do count_variable = initial_value, final_value, step_size
Block of statements
end do
count_variable : must be an integer
initial_value, final_value : are arbitrary expressions of
integer type
step_size = 1
(default)
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do
construct
do count = initial, final, inc
block of statements
end do
loop
count_variable : must be an integer
initial_value, final_value : are arbitrary expressions
of integer type
selected step_size = inc : must be an integer
9
Example
do number = 1, 10, 2
print *, number, number **2
end do
print *, number, number **2
OUTPUT produced will display following results :
1
1
3
9
5
25
7
49
9
81
10
Examples
do statement
iteration count
do variable values
do i = 1,10
10
1,2,3,4,5,6,7,8,9,10
do j = 20, 50, 5
7
20,25,30,35,40,45,50
do p = 7, 19, 4
4
7,11,15,19
do q = 4, 5, 6
1
4
do r = 6, 5, 4
0
(6)
do x = -20,20, 6
7
-20,-14,-8,-2,4,10,16
do n = 25, 0, -5
6
25,20,15,10,5,0
do m = 20, -20, -6
7
20,14,8,2,-4,-10,-16
do number = 1, 10, 2
print *, number, number **2
end do
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DO LOOP – TYPE 2
(controlled by logical expression)
The number of iterations cannot be determined in
advance, and a more general repetition structure is
required.
Number=0
Do
do
Block of statements_1
if ( logical_expression) then
exit
Number=number+1
if (number>100) then
exit
else
Print *, number, number **2
else
block of statements_2
end do
endif
end do
12
!Please calculate sum and ave of given number students grade.
program sumandaveofstudentgrade
real::note,notesum,noteave
integer::number,i
notesum=0
print*,"How mony student grade you want calculate"
read*,number
do i=1,number
print*,"Please enter grade of student",i
read*,note
notesum=notesum+note
end do
print*,"Sum of students grade is:",notesum
noteave=notesum/number
print*,"Average of students grade is:",noteave
end program sumandaveofstudentgrade
13
Program temp_fahr_conv
real::t,f
t=0
do
t=t+1
if (t>100) then
exit
end if
f=t*1.8+32
write(unit=*,fmt=“(f5.1,a,f7.2,a)”)t,”C=”,f,”F”
end do
end program temp_fahr_conv
14
Count-controlled do loops
do count = initial, final, inc
do count = initial, final (inc = 1)
Do
Integer variable
Iteration count:
How many times we will go through the loop?
max((final-initial+inc)/inc, 0)
iterations = ( stop + step - start ) / step
15
NESTED DO - LOOPS
The body of a do loop may contain another do loop. In this
case,the second do loop is said to be “nested” within the first
do loop.
EXAMPLE :
do m = 1, 4
do n = 1, 3
product 1 = m * n
Write(unit=*,fmt=“(3i5)” )m,n,product1
end do
end do
OUTPUT
m
n
1
1
1
1
2
2
1
3
3
2
1
2
2
2
4
2
3
6
3
1
3
3
2
6
3
3
9
4
1
4
4
2
8
4
3
12
product
16
More flexibility...
For do – loops especially defined as Type 1, it is
needed a control statement in order to control the
cycles, otherwise it is possible to have an “infinite
loop”.
Using the command “ exit “ all the remaining
statements in the loop are omitted and thus, a transfer of
control following the “ end do ” statement is obtained.
Thus, an “exit“ statement can cause termination of a
current/indexed
do - construct before the do variable value goes beyond
the final or limit value.
17
Some flexibility...
do
.
.
.
if (condition) then
exit
end if
.
.
.
end do
.
18
Some more flexibility...
As mentioned before, exit statement causes
repetition of a loop to terminate by transfering control
to the statement following the “end do”.
On the other hand, sometimes it is necessary to
terminate only the current repetition and then jump
ahead to the next one.
F provides the “cycle” statement for this purpose.
19
Some more flexibility...
do
.
.
.
if (condition) then
cycle
end if
.
.
.
end do
.
20
PROBLEM : Suppose that in the temprature-conversion only temprature of 0oC or above values are
wanted to convert.
program convert1
real::celcius,fahr
character(len=1)::kontrol
do
print"(a)","Sicaklığı Cel cinsinden giriniz : cikis icin Q giriniz"
read"(f5.1)",celcius
if ( celcius < 0.0 ) then
print *, " given temprature must be 0.0 or above"
cycle
else
fahr=celcius*1.8+32
print*,celcius," is ",fahr
print*,"Cikis icin Q"
read*,kontrol
if (kontrol=="Q") then
exit
end if
endif
end do
end program convert1
21
Naming your do constructs
Especially in “nested do–loops” it’s very difficult to control the
transfer of the program. As mentioned before an “exit“
statement in the example seen below, will transfer control to
the first executable statement following the second “ end do
”.
On the other hand, there will be occasions when it is required
to exit from all of the enclosing loops; or even from more than
the immediately enclosing or current loop, but not from all of
them.
For this reason it is strongly recommended to use “named do
– constructs” by preceding the do statement by a name as is
seen below :
[name:] DO [control clause]
block
END DO [name]
22
Naming your do constructs
outer: DO i=1,10
inner1: DO
IF( x<0 ) EXIT ! exit loop inner1
IF( x==0 ) EXIT outer ! exit loop outer
...
END DO inner1
inner2: DO
IF( x<0 ) CYCLE ! cycle loop inner2
IF( x==0 ) CYCLE inner1 ! illegal
...
END DO inner2
...
END DO outer
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number: DO i=1,100
WRITE(*,*) i ! write numbers 1 to 100
END DO number
dontwrite: DO j=100,1
WRITE(*,*) j ! no WRITE statement executed
END DO dontwrite
decr: DO k=100,1,-3
WRITE(*,*) k ! write numbers 100,97,94
END DO decr
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INTEGER :: value=0, total=0 ...
sum: DO
READ(*,*) value ! read in a number
IF (value==0) EXIT sum ! if nothing to add, exit loop
total = total + value ! calculate running total
END DO sum
program doloop
integer::ii,istart=1,ilast=100,istep=3,isum
do ii=istart,ilast,istep
isum = isum + ii
print*,isum
End do
end program doloop
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Dealing with exceptional situations:
There are occasionally situations in which the statements used
before are inconvenient or make programming very difficult.
Thus, two additional statements exist to help us in these
exceptional situations. These are,
STOP : this statement terminates the execution without to need
to find a way of reaching the “end” statement of the main
program unit. This word “stop” causes execution of the program
to be terminated immediately.
RETURN : this statement causes a return from a procedure
without the need to find a way of reaching the “end” statement of
the procedure. This word “return” causes execution of the
procedure to be terminated immediately and control transferred
back to the program unit which called or referenced the
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procedure.
Dealing with exceptional situations:
• stop statement
– simply terminates execution
• return statement
– causes execution of the procedure to be
terminated immediately and control
transferred back to the program unit
which called or referenced the
procedure
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Syntax examples of control constructs:
if (number > maximum) then
number = maximum
else if (number < minimum) then
number = minimum
end if
select case (n+no)
case (3)
x = 34.3
case default
x = 1.0 / x
end select
do j = 1,100
if ( j <= 50) then
k = j - 4 print *, k cycle end if print *, j
end do
doname: do
if ( value > climate_index) then
exit doname
end if
value = new_value
end do doname
28
program can_pressure
! This program calculates the pressure inside the can
real :: T,pressure
T=15.0
control:do
T=T+1
pressure=(0.00105*(T**2))+(0.0042*T)+1.352
if (pressure>3.2) then
exit control
end if
print *,"The pressure inside the can is",&
pressure," atm at",T," degree C"
end do control
end program can_pressure
29
program examination_marks
!
This program prints statistics about a set of exam results
!
variable declerations
integer :: i,number,mark,maximum,minimum,total
real :: average
!
initialize variable
total = 0
!
read number of marks , and then the marks
print *,"how many marks are there"
read *,number
print *," please type ",number," marks, one per line"
!
Loop to read and process marks
do i = 1 , number
read *, mark
!
initialize max. and min. marks for only the first loop.
if (i==1) then
!
this if construct is executed for the case only i=1.
maximum = mark
minimum = mark
end if
!
on each pass ,update sum,maximum and minimum
total = total + mark
if (mark > maximum)then
maximum = mark
else if (mark < minimum)then
minimum = mark
end if
end do
!!
calculate average mark and print out results
average = real(total) / number
print *,"highest mark is",maximum,"lowest mark is",minimum,"average mark
30
is",average
end program examination_marks
program lever
! This program calculates the effort required for levers of
lengths
! differing in steps 2 metres
integer ,parameter :: load=2000,d2=2
integer :: d1,n,m
real :: effort
print *,"please type the min limit of distance n and max limit c m"
read *,n,m
do d1 = n , m , 2
effort = real(load)*real(d2)/real(d1)
print *,"The required effort when d1=",d1," m."," is",effort," kg"
end do
end program lever
31
!This program written to understand do loop
program loop_test1
integer :: i,j,k,l,m,n
i=1
j=2
k=4
l=8
m=0
n=0
do i=j,k,l
k=i
do j=l,m,k
n=j
do k=l,n
do l=i,k
m=k*l
end do
end do
end do
end do
print *,i,j,k,l,m,n
end program loop_test1
32
!Write a program to calculate the international paper sizes
program paper_size
integer :: n
real :: cm,inch,p1,p2
do n = 0,6
p1 = 0.25 - n/2.0
p2 = -0.25 - n/2.0
cm = (2.0**p1 * 2.0**p2)*100.0
inch = cm/2.54
print *,"A",n," is",cm," cm"," and",inch," inch"
end do
end program paper_size
33
!Write a program to calculate TAX depending on total income
program exercise_2
!taxation parameter declarations
integer, parameter ::first=5000,second=15000
real,parameter::first_per=0.10,second_per=0.25,next_per=0.30
!variable declaration
integer :: income, total_tax
!read the income
print *," Type total income in US dollars"
read *, income
!do if blocks
if (income <= first) then
!first slice
total_tax = first_per*income
else if (income > first .and. income < second) then
total_tax = second_per*income
else
total_tax = next_per*income
end if
!print the result
print *," total income =
",income
print *," total tax charged = ",total_tax
end program exercise_2
???
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