ICS 101 Introduction to Computer Programming LAB 6

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ICS 101 Introduction toComputer ProgrammingLAB
6

• Zeehasham Rasheed
• hasham_at_ccse.kfupm.edu.sa
• Information Computer Science Department King
  Fahd University of Petroleum Minerals

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Lab 6

• Review of Functions
• IF Statement with Functions
• Special Cases of Functions
• Intrinsic Function
• Statement Function
• Example
• Exercises

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Review of Functions

• Already discussed in Lab 5, Review following lab

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Function Sub-programs

• Function Subprogram is the description of a
  function consisting of several statements.
• The subprogram (in the case of function) computes
  a single value and stores that value in the
  function name.
• A function subprogram consists of a function
  header and a function body

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Function Sub-programs (Contd)

• Function Header
• Format
• type FUNCTION fname (a list of arguments)
• where
• type is the type for the function name i.e. REAL,
  INTEGER
• fname is the name of the function (6 variable)
• a list of arguments is the optional list of
  arguments
• if the type of the function is not specified, the
  function type is assumed as either INTEGER or
  REAL.
• Rules that apply to naming a variable also apply
  for function name
• If there are no arguments to a function, then the
  empty parentheses () appear with the function
  name

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Function Sub-programs (Contd)

• Function Body
• Format
• The function Body is similar to a FORTRAN program
• Must end with END statement
• The Return statement must appear in the function
  body atleast once.

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Function Sub-programs (Contd)

• General form of the function
• TYPE FUNCTION FNAME ( A LIST OF DUMMY ARGUMENTS)
• DECLARATION OF DUMMY ARGUMENTS AND VARIABLES TO
  BE USED IN THE FUNCTION
• EXECUTABLE STATEMENTS
• ..
• FNAME EXPRESSION
• ..
• ..
• RETURN
• END

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Function Sub-programs (Contd)

• Example To compute Volume of a sphere with
  radius RADIUS
• REAL FUNCTION VOLUME (RADIUS)
• REAL RADIUS, PI
• PI 22.0/7
• VOLUME 4.0 / 3.0 PI RADUIS 3
• RETURN
• END

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Function Call and Rules

• Actual and dummy arguments must match in type,
  order and number. The names of these arguments
  may or may not be same.
• Actual Arguments ( that is appear in a calling
  segment) can be expressions, constants or
  variable names.
• F(AB)
• ORDER (3,2,4)
• ORDER (3,42, 99)
• F(A)
• BUT Dummy arguments must be variable names and
  should never be expressions or constants.

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Function Call and Rules (Contd)

• The type of the function name must be the same in
  both the calling program and the function
  description
• The result from the function subprogram, to be
  returned to the calling program, should be stored
  in the function name.
• Atleast one return statement in each subprogram
  should be there.
• A function may be placed either before or after
  the main program, not in the middle.
• A Fortran function cannot call itself.
• A function is called or invoke in a main program
  or in other subprogram as part of an expression

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Example

• C Main program
• INTEGER X, Y, Z, SUM
• READ, X, Y, Z
• PRINT, SUM(X, Y, Z)
• END
• C Function Subprogram
• INTEGER FUNCTION SUM(A, B, C)
• INTEGER A, B, C
• SUM A B C
• RETURN
• END

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IF Statement with Functions

• Write a program, which takes two digit number as
  input and reverse the digits. Implement it with
  the help of function and also write a conditional
  construct which takes cares of condition that
  only two digit positive number is taken as input.
  Also function should return an error code -1 if
  the argument is not two digit number.

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• INTEGER FUNCTION RVSNUM(NUMBER)
• INTEGER NUMBER, RDIGIT, LDIGIT
• IF(NUMBER .LT. 10 .OR. NUMBER .GT. 99 ) THEN
• RVSNUM -1
• RETURN
• ENDIF
• LDIGIT NUMBER / 10
• RDIGIT NUMBER - LDIGIT 10
• RVSNUM RDIGIT 10 LDIGIT
• RETURN
• END

C MAIN PROGRAM INTEGER NUMBER, RVSNUM,
RNUM READ, NUMBER RNUM RVSNUM(NUMBER) IF(RNU
M .EQ. -1) THEN PRINT, 'INPUT ERROR
',NUMBER ELSE PRINT, 'ORIGINAL NUMBER IS ',
NUMBER PRINT, 'REVERSED NUMBER IS ',
RNUM ENDIF END
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Special Cases of Functions

• There are special cases of functions that do not
  require subprogram description.
• Intrinsic (Built-in) Functions
• Statement Function

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Intrinsic Functions

• These are predefined functions that are available
  from the FORTRAN language.
• They are mostly mathematic functions
• Example
• SQRT(X) Square root of real number X, return
  REAL
• ABS(X) Absolute value of X, return integer
• SIN(X) Sine of angle X (angle is in radians).
  return REAL
• EXP(X) e raised to the power X, return REAL
• LOG(X) Natural Log of real number X, return REAL
• LOG10(X) Log of real number X with base 10,
  return REAL
• MOD(M,N) Remainder of M/N, integer argument,
  return integer

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Statement Functions

• Functions that can be write in a single
  statements
• They are alternate to the function subprogram
• A statement function is defined in the beginning
  of a program but after declaration statements
• As a non-executable statement, it should appear
  before any executable statement.
• General Form
• fname ( a list of arguments, which should
  declared previously) expression
• fname is the name of the functions
• a list of arguments is the optional list of dummy
  arguments
• expression computes the function value
• One can note that type is not declared here
• Type of fname should be declared just like other
  variables in the argument list or it will be
  implicitly defined

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Statement Functions (Contd)

• Example
• Write a statement function to compute the area of
  a triangle, given its two sides and an angle
• REAL AREA, SIDE1, SIDE2, ANGLE
• AREA(SIDE1, SIDE2, ANGLE) 0.5 SIDE1
  SIDE2 SIN (ANGLE)
• Write a statement function to compute the total
  number of seconds, given the time in hours,
  minutes and seconds
• REAL TOTSEC, HOUR, MINUTE, SECONDS
• TOTSEC (HOUR, MINUTE, SECOND) 3600 HOUR
  60 MINUTE SECOND

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Statement Functions (Contd)

• Write a program which computes the function F(X,
  Y) 3 X 2 5 X Y
• REAL F, X, Y
• F(X,Y) 3 X 2 5 X Y
• PRINT, 'Input two real numbers'
• READ, X, Y
• PRINT, 'Output of function 3 X 2 5 X
  Y ', F(X,Y)
• PRINT, 'INPUTS are ', X, ' and ', Y
• END

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Statement Functions (Contd)

• Syntax error will occur if used at somewhere else
  in the program
• Proper placement is necessary
• If type is not mentioned in the declaration of
  the function name, implicit type will be assumed
  depending on the name of the function name (same
  case as in variable)

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Exercise

• With the help of the INTRINSIC function, find the
  square root of the positive real. With the help
  of conditional construct be sure to input the
  positive number.

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Exercise

• With the help of the INTRINSIC function, find the
  logarithm to the base 10 of the positive real.
  With the help of conditional construct be sure to
  input the positive number.

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Exercise

• Rewrite the following function in terms of
  statement function
• REAL FUNCTION AREA(CIRCUM)
• REAL CIRCUM, RADIUS, PI
• PI 3.14159
• RADIUS CIRCUM/(2.0PI)
• AREA RADIUS 2 PI
• RETURN
• END

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Exercise

• Implement and Tell me the Flow of the following
  program
• INTEGER FUNCTION MAXA(M,N)
• INTEGER M, N
• IF ( M .GT. N) THEN
• MAXA M
• ELSE
• MAXA N
• ENDIF
• RETURN
• END
• INTEGER NUM1, NUM2, MAXA, ANS
• PRINT, ' INPUT TWO NUMBERS WHICH ARE INTEGER '
• READ, NUM1, NUM2
• IF (NUM1 .NE. NUM2) THEN
• ANS MAXA(NUM1,NUM2)
• PRINT, ' Maximum number is ', ANS