Arithmetic Operators

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Arithmetic Operators

• Arithmetic Operations with
• Variables

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Arithmetic Operators

• Name Operator Example
• Addition num1 num2
• Subtraction - initial - spent
• Multiplication fathoms 6
• Division / sum / count
• Modulus m n

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Arithmetic OperatorsInfix Notation

• Operator is between the operands
• y a b (c d)
• Resembles standard mathematical notation
• Requires parentheses to show order.

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Modulus

• The expression m n yields the remainder after
  m is divided by n.
• Modulus is an integer operation. - Both operands
  MUST be integers.
• Examples 17 5 2
• 6 3 0
• 9 2 1
• 5 8 5

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Modulus

• 11 4 11 2 4 3 ? 11 4 3
• 31 27 ?
• 16 9 ?
• 32 5 ?
• 64 21 ?
• 128 31 ?

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Uses of Modulus

• Even and Odd
• 5 2 1 odd 4 2 0 even
• Take the modulus by 2 of any integer, a result of
  1 means the number was odd, a result of 0 means
  the number was even.
• The Euclidean GCD algorithm

7
Integer Division

• If both operands of a division expression are
  integers, you get an integer answer. The
  fractional portion is thrown away, not rounded!
• Examples 17 / 5 3
• 4 / 3 1
• 35 / 9 8
• 3 / 4 0
  (!)

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Mixed Division

• Division where one operand is a floating point
  number will produce a floating point result.
• Integer is promoted to a float
• Division where one operand is a double will
  produce a double result.
• Integer is promoted to a double.
• General rule promotion to highest type

9
Division By Zero

• Division by zero is mathematically undefined.
• Division by zero will cause a fatal error. ---
  your program will terminate immediately and give
  an error message.
• Often caused by forgetting to initialize
  variables (or using zero result of integer
  division).

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Non-Fatal Errors

• Non-fatal errors will not cause program
  termination, but they may produce incorrect
  results.

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Precedence and Associativity

• Many ways to interpret arithmetic statements
• 5 7 3 2 41 ? 76 ? 65 ? 100
• Infix notation is inherently ambiguous, need
  rules of precedence and associativity

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Arithmetic Operators Rules of Operator Precedence

• Operator(s) Precedence Associativity
• ( ) Evaluated first. If nested - innermost
  first. If on same level - left to right.
  
• / Evaluated second. If
  several, evaluated left to right
• - Evaluated third. If there are
  several, evaluated left to right.
• Evaluated last, right to left.

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Evaluation of expressions

• a b c Would multiply a b first, then
  add c to the result.
• If we really want the sum of b and c to be
  multiplied by a, use parenthesis to force the
  evaluation to be done in the order we want.
• a ( b c )

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Practice With Evaluating Expressions

• Given integer variables a, b, c, d, e, where a
  1, b 2, c 3, d 4
• Evaluate the following expressions
• a b - c d
• a b / c
• 1 a b c
• a d b - c
• e d c / b - a

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Good Programming Practices

• You will be given a handout of suggested C coding
  standards and Indentation Styles
• You will be expected to conform to these
  standards for all programming projects in this
  class.
• Pick one of the two indentation styles shown and
  use it consistently.

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A Sample Project

• Project We are going to write a program
  in class that finds the volume and surface
  area of a box.
• Write the Algorithm
• Use the algorithm as a guide for writing the
  code.

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An algorithm for writing code

• Write the algorithm
• Write the code using emacs
• Try to compile the code
• While there are still syntax errors
• Fix errors
• Try to compile the code
• Test the program
• Fix any semantic errors
• Compile the code
• Test the program