Introduction to Algorithmic Processes CMPSC 201C Fall 2000

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Introduction to Algorithmic ProcessesCMPSC
201CFall 2000
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Administrative Issues

• Exam 2 - Monday, November 6 at 815 to 930 in
  102 and 105 Forum
• Sections 3, 4, 5, 6, 9,and 10 (John and Pyush)
  will be in 102 Forum and sections 1, 2, 7, 8,
  11,and 12 (Anand and Nidhi) will be in 105 Forum.
• Conflict form must be returned to me by noon on
  October 25!
• Two practice exams will be on web and I-drive by
  October 25.

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Types of parameters

• Formal parameters(arguments) - parameters listed
  in the function heading
• Actual parameters(arguments) - parameters listed
  in the function call

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Example Cont.

• //Function to calculate miles per gallon for a
  tank of gas.
• //
• int mpg(double oldOdom, double newOdom,
• double gallons) // function heading
• int ans (int) ((newOdom - oldOdom)/gallons))
• return ans

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Scope

• Scope - portion of code in which the identifier
  name is accessible.
• Local - limited to a specific block of statements
  in which the identifier was declared (or defined
  for a function name)
• Global - may be accessed from any portion of code
  once the identifier has been declared (usually at
  beginning of code).
• Usually variables are local and constants are
  global.
• If you do use global variables, be VERY careful
  as they can be affected in ways you did not
  expect.

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Block

• Statements that are enclosed braces .
• May be body of function, loop, if-then, etc.

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Scope Rules

• A name that is declared within a block is local
  to that block and is accessible only within that
  block.
• All other names are inherited from the
  immediate surrounding region.

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Lifetime

• Lifetime of a variable or constant is the time
  when memory has been allocated to it.
• If the constant or variable is global, memory is
  always allocated to that constant or variable and
  the lifetime would be static.
• If the constant or variable is local, then memory
  is only allocated when the block in which it was
  declared is executing and the memory is
  deallocated when the block is finished executing.
  In this case the lifetime would be automatic.

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Program Example
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Questions????
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Multiple Results

• Value- returning function returns one value to
  the function that called it.
• However, sometimes more that one result is
  calculated and need to be passed back to the
  originating function.
• Then use reference parameters (arguments) in the
  formal parameter list.

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Example (pg. 149)

• // Add two vectors that are at right angles..
• // Pi is a global CONSTANT that was declared
  before
• // main
• void addVect (double a, double b //vectors at rt
  lts
• double rMagnitude // output
• int rDirection ) // output - direction
• double rDirRadians //local variable
• rMagnitude sgrt(a a b b)
• rDirRadians atan (b / a)
• rDirection (int) (180 / Pi rDirRadians
  0.5)

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Function Heading

• Pass by value
• int mpg(double oldOdom, double newOdom,
• double gallons)
• Pass by reference
• void addVect (double a, double b //vectors at rt
  lts
• double rMagnitude // output
• int rDirection ) // output - direction

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Function Prototype

• Pass by value
• int mpg (double, double, double)
• Pass by reference
• void addVect (double, double, double, int)

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Function call

• Pass by value
• lastTankMPG mpg(10502.5, 10754.6, 10.0)
• Pass by reference
• addVect (aVect, bVect, rMag, rDir)

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Pass by reference

• When using pass by reference, both identifiers
  (the one in the function call and the one in the
  function heading) refer to the same memory
  location.
• Therefore, when formal parameter (the one in the
  function) changes what is stored in the memory
  location, the same change occurs for the actual
  parameter

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Formal and Actual Parameters

• Formal Parameter Actual Parameter
• Pass by value value, variable, or an
• expression
• Pass by reference variable

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Value vs Nonvalue

• Use value-returning functions (int, float,
  double, etc.) when one value needs to be passed
  back to the calling function.
• Use nonvalue-returning functions (void) for
  printouts, pass multiple results, modify actual
  parameters.
• See table 5.2 on page 153

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Questions????
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Recursive Function

• A function that calls itself or is part of a
  cycle of calls.

f1
f1
f3
f2
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Non-programming Example

• Recursive definition of a cow.
• A cow is a four-legged animal whose mother was a
  cow.

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