FORTRAN 90
Lecture : Rafel Hekmat Hameed
University of Babylon
Subject : Fortran 90
College of Engineering
Year : Second B.Sc
Mechanical Engineering Dep.
1. INTEGER DIVISION
10 / 3 evaluates to 3
19 / 4 evaluates to 4
4 / 5 evaluates to 0 (which could cause an unwanted division by zero)
- 8 / 3 evaluates to -2
3 * 10 / 3 evaluates to 10
10 / 3 * 3 evaluates to 9
2. Mixed-mode expressions
10 / 3.0 evaluates to 3.33333
4. / 5 evaluates to 0.8
2 ** (- 2) evaluates to 0 (?)
However, note that
3 / 2 / 3.0
Evaluates to 0.333333 because 3 / 2 is evaluated first, giving integer 1.
3. Numeric Assignment
If expr is not of the same type as var, it is converted to that type before
assignment. This means that there might be loss of precision. For example
,assuming N is integer, and X and Y are real:
N = 10. / 3 (value of N is 3)
X = 10 / 3 (value of X is 3.0)
Y = 10 / 3. (value of Y is 3.33333)
ϭ
4. Flowchart
A flowchart is a type of diagram that represents an algorithm or process,
showing the steps as boxes of various kinds, and their order by connecting these
with arrows.
Flowchart symbol
Symbol
Description
Start or stop point in process.
An operation or action step.
A question or branch in the process.
Indicates data inputs and outputs to and
from process.
A preparation or set-up process step.
Connector a jump from one point to
another.
Continuation onto another page.
Indicated the direction of flow for
materials and/or information.
Flowchart for computing the factorial
N!=(1234567..10) represented below
Ϯ
of
N
(10!)
where
start
Read N
Dсϭ
&сϭ
F=F. M
DсDнϭ
No
IS
M=N ?
Yes
PRINT F
End
5.Relational Operators
There are six relational operators:






<:
<= :
>:
>= :
== :
/= :
.LT.
.LE.
.GT.
.GE.
.EQ.
.NE.
less than
less than or equal to
greater than
greater than or equal to
equal to
not equal to
Important rules:

Each of these six relational operators takes two operands. These two
operands must both be arithmetic or both be strings. For arithmetic
operands, if they are of different types (i.e., one INTEGER and the other
REAL), the INTEGER operand will be converted to REAL.
ϯ


The outcome of a comparison is a LOGICAL value. For example,
5 /= 3 is .TRUE. and 7 + 3 >= 20 is .FALSE.
All relational operators have equal priority and are lower than those of
arithmetic's operators.
Example
a + b /= c*c + d*d
Expressions a+b and c*c + d*d are evaluated before the relational operator /=
is evaluated.
Examples



3**2 + 4**2 == 5**2 is .TRUE.
If the values of REAL variables a, b and c are 1.0, 2.0 and 4.0,
respectively, then b*b - 4.0*a*c >= 0.0 is equivalent to 2.0*2.0 - 4.0*1.0*4.0
>= 0.0, which evaluates to -12.0 >= 0.0. Thus, the result is .FALSE.
If REAL variables x and y have values 3.0 and 7.0, and INTEGER
variables p and q have values 6 and 2, what is the result of
x*x - y*y + 2.0*x*y /= p*q + p**3 - q**3?
6. LOGICAL Operators and Expressions
Fortran has five LOGICAL operators that can only be used with
expressions whose results are logical values (i.e., .TRUE. or .FALSE.). All
LOGICAL operators have priorities lower than arithmetic and relational
#_>
#_>
operators. Therefore, if an expression involving arithmetic, relational and logical
operators, the arithmetic operators are evaluated first, followed by the relational
operators, followed by the logical operators.
These five logical operators are





.NOT.
.AND.
.OR.
.EQV.
.NEQV.
: logical not
: logical and
: logical or
: logical equivalence
: logical not equivalence
ϰ
The priority of .NOT. is the highest, followed by .AND., followed by
.OR., followed by .EQV. and .NEQV.
Note that .NOT. is right associative, while the other four are left
associative.
Examples
Let LOGICAL variables Something and Another have values .TRUE.
and .FALSE., respectively.
.NOT. Something .AND. Another
--> .NOT. .TRUE. .AND. .FALSE.
--> [.NOT. .TRUE.] .AND. .FALSE.
--> .FALSE. .AND. .FALSE.
--> .FALSE.
Let LOGICAL variables a, b and c have values .TRUE., .TRUE. and
.FALSE., respectively.
.NOT. a .OR. .NOT. b .AND. c
--> .NOT. .TRUE. .OR. .NOT. .TRUE. .AND. .FALSE.
--> [.NOT. .TRUE.] .OR. .NOT. .TRUE. .AND. .FALSE.
--> .FALSE. .OR. .NOT. .TRUE. .AND. .FALSE.
--> .FALSE. .OR. [.NOT. .TRUE.] .AND. .FALSE.
--> .FALSE. .OR. .FALSE. .AND. .FALSE.
--> .FALSE. .OR. [.FALSE. .AND. .FALSE.]
--> .FALSE. .OR. .FALSE.
--> .FALSE.
Let INTEGER variables m, n, x and y have values 3, 5, 4 and 2,
respectively, what is the result of the following expression?
.NOT. (m > n .AND. x < y) .NEQV. (m <= n .AND. x >= y)
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