CS1001 Lecture 5

1
CS1001 Lecture 5

• Completion of Lecture 4
• Talked about Data Types Arithmetic Errors
• Continue with Operations and Functions
• Program Testing Tips
• File Input and Outputs

2
Data Types In Fortran

• Integer (0, 137, -2516, 17745)
• Real or Single Precision (0.0, -0.01536, 123.4,
  1.234E2, -1.536E-2)
• Double Precision (1.234D-6, 0.1111111D3)
• Complex (34i)
• Character Strings (A, JOHN DOE)
• Logical (.TRUE., .FALSE.)

3
Arithmetic Operations

• Binary Unary
• Addition positive
• - Subtraction - negative
• Multiplication e.g., 5.0 (-1)
• / Division
• Exponentiation
• Precedence Rules
• 0. Parenthesis
• 1. Exponentiation, right to left
• 2. Multiplication and Division, left to right
• 3. Addition and subtraction, left to right

4
Operations

• Operations result in same type as operands
• 6/5 1 integer operation (Division of integers
  produces an integer)
• 6.0/5.0 1.2
• Mixed-Mode expressions -- combine integer and
  real data
• e.g. 1.0/4 gt 1.0/4.0 gt 0.25
• 3.08/5 gt 3.01 gt 3.01.0 gt 4.0
• 3.08.0/5 gt 3.01.6gt4.6
• Generally poor practice

5
Assignment Statement

• variable expression
• e.g., Height 0.5accelerationtime2
• initialvelocitytimeinit
  ialheight
• Velocityaccelerationtimeinitialvelocity
• NOT an algebraic equality, but a replacement
  statement
• sum sum x means add the value of x to the
  value of sum and store the result in sum.

6
Arithmetic Functions

• Perform standard operations on variables which
  are referenced as an argument
• Standard arithmetic functions do not have to be
  declared, merely used (see page 60 of text)
• Examples COS(X), SQRT(X), LOG(X)
• PROGRAM MiddleOfRange
• Print , enter 10 measures
• Read , x1,x2,x3,x4,x5,x6,x7,x8,x9,x10
• MidRange ( MAX(x1,x2,x3,x4,x5,x6,x7,x8,x9,x10)
  
• MIN(x1,x2,x3,x4,x5,x6,x7,x8,x9,x10) )
  / 2.
• Print , Mid Range is , MidRange
• END PROGRAM MiddleOfRange

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PROGRAM QuadraticEquations_1 !--------------------
----------------------- ! Program to solve a
quadratic equation ! using the quadratic
formula. ! Variables used are ! A, B, C
the coefficients of !
the quadratic equation ! Discriminant the
discriminant, ! B2 -
4.0AC ! Root_1, Root_2 the two roots of
the ! equation ! ! Input
The coefficients A, B, and C ! Output The two
roots of the equation or ! the
(negative) discriminant and a ! message
indicating that there are ! no real
roots !-------------------------------------------
--
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IMPLICIT NONE REAL A, B, C, Discriminant,
Root_1, Root_2 ! Get the coefficients PRINT
, "Enter the coefficients of the
quadratic equation" READ , A, B, C !
Calculate the discriminant Discriminant B2
- 4.0AC
9
Preview of next lecture
Control flow
Sequential execution
Statement_1
Statement_1
Statement_2
If
.
.
.
Statement_n
Statement_2
Statement_3
Statement_4
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! Check if discriminant is nonnegative. If !
it is, calculate and display the roots. !
Otherwise display the value of the !
Discriminant and a no-real-roots message. IF
(Discriminant gt 0) THEN Discriminant
SQRT(Discriminant) Root_1 (-B
Discriminant) / (2.0 A) Root_2 (-B -
Discriminant) / (2.0 A) PRINT , "The
roots are", Root_1, Root_2 ELSE PRINT ,
"Discriminant is", Discriminant PRINT ,
"There are no real roots" END IF END PROGRAM
QuadraticEquations_1
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Consider Hungarian Notation

• iName for INTEGER variables/constants
• rName for REAL
• dName for DOUBLE PRECISION
• xName for COMPLEX
• cName for CHARACTER strings
• bName for LOGICAL (boolean)
• Constants are all caps except type (rVAL)

12
Simple List-Directed Output

• PRINT , output-list where output-list is
• output-list can contain multiple items
• A constant such as ENTER TIME
• A variable such as OUTPUT
• A formula or function such as SQRT(INP)
• The indicates that the output format is
  free-form, or whatever the memory holds for that
  value, which may be truncated
• e.g., PRINT , Square root of , x, ,
  SQRT(x)
• Square root of 4.00 2.00

13
Simple List-Directed Input

• READ , input-list, where input-list is
• A variable or variables
• The user should be prompted for all inputs with a
  PRINT statement, and units and/or ranges should
  also be specified to the user inputing the data

14
File I/O (Input/Output)

• So far, free form READ and PRINT -- input from
  keyboard and output to display
• For input and output of larger amount of data,
  file I/O may be used.
• First, must let computer know what the files are
• OPEN (UNITunit_number,FILEfile_name,STATUSstatu
  s)
• unit_number is an integer to be used by READ and
  WRITE
• file_name is string of the name of file
• status is string OLD for existing files or
  NEW for new file
• e.g., OPEN(UNIT10,FILEinput_data,STATUSOLD
  )
• OPEN(UNIT11,FILEout_data,STATUSNEW)

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File I/O

• Input
• READ (unit_number,) input_list
• unit_number is digit specified in OPEN statement
• e.g., File input_data contains three resistance
  values and one voltage value
• 1.0, 1.0, 1.0
• 6.0
• OPEN(UNIT10,FILEinput_data,STATUSOLD)
• .
• READ(10,) resistance_1, resistance_2,
  resistance_3
• READ(10,) voltage

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File I/O

• Output
• WRITE (unit_number,) output_list
• unit_number is digit specified in OPEN statement
• e.g., File current_data is the output file
• OPEN(UNIT11,FILEcurrent_data,STATUSNEW)
• .
• WRITE(11,) The current is, current, amps
• File current_data is created and contains the
  line
• The current is 18.0000000 amps

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• PROGRAM Projectile_2
• !------------------------------------------------
• ! This program calculates the velocity and height
  ! of a projectile given its initial height,
• ! initial velocity, and constant acceleration.
• ! Identifiers used are
• !InitialHeightinitial height of projectile
  (meters)
• !Height height at any time (meters)
• !InitialVelocity initial vertical velocity
  (m/sec)
• !Velocity vertical velocity at any time
  (m/sec)
• !Accelerationconstant vertical acceleration
• ! (m/sec/sec)
• !Time time since launch (seconds)
• !
• ! Input (file) InitialHeight, InitialVelocity,
  Time
• ! Output (file) Velocity, Height
• !-------------------------------------------------
  ----

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Specification
IMPLICIT NONE REAL InitialHeight, Height,
InitialVelocity, Velocity, Time REAL,
PARAMETER Acceleration -9.80665 ! Open
disk files FIG2-6.DAT and FIG2-6.OUT OPEN(UNIT
12, FILE "FIG2-6.DAT", STATUS "OLD")
OPEN(UNIT 13, FILE "FIG2-6.OUT", STATUS
"NEW") ! Read values for InitialHeight,
InitialVeloc, ! and Time READ (12, )
InitialHeight, InitialVelocity, Time !
Calculate the height and velocity Height 0.5
Acceleration Time 2
InitialVelocity Time InitialHeight Velocity
Acceleration Time InitialVelocity
Execution
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! Write values of Time, Velocity, and Height !
to FIG2-6.OUT WRITE (13, ) "At time", Time,
"seconds" WRITE (13, ) "the vertical velocity
is", Velocity, "m/sec" WRITE (13, )
"and the height is", Height, "meters" ! Signal
user that program is finished PRINT , "
Program is finished " END PROGRAM
Projectile_2
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Arithmetic Errors

• Overflow and underflow errors
• 8 bit exponent restricts range to about 38 to -38

10(-38)
0
-10-38
-1038
1038
overflow
overflow
underflow
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Roundoff errors

• Due to binary representation and finite number of
  bits
• (AB)C (1000. 0.4)0.3 1000.7
• (AB) gt 1000. 0.4000 gt 1000.
• The result of (AB) added to C gt 1000. 0.3000
  gt 1000.
• A (BC) 1000. ( 0.4000 0.3000)
• (BC) .4000 .3000 gt .7000
• Add A to (BC) gt 1000. .7000 gt 1001.
  (rounding up)
• (AB) C A (BC)

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Program Testing Tips

• Boundary/bounds check all inputs
• 1-100 input range, check 1, 100, 101, 0
• Check upper and lower case if applicable
• Quadrant test in all four quadrants
• 45, 135, 225, 315 degrees
• Type test data inputs
• Enter 10.5 for an INT, 56 for a REAL, etc.
• Have someone else test your program, and
  reciprocate