Arithmetic Expressions

1
Arithmetic Expressions

• Reading Chapter 2

2
Arithmetic Expression

• Anything reducible to a single value
• Consists of constants and/or variables connected
  by arithmetic operators
• Each expression can be evaluated to compute a
  value of a given type

3
Operator Types

• binary involving 2 operands 2 3
• unary involving 1 operand -3
• ternary involving 3 operands later

4
Precedence/Associativity

• Precedence determines which operator is applied
  first in an expression having several operators.
• Associativity dictates the order if two operators
  have the same precedence.
• left to right the left operator applied first
• right to left the right operator applied first

5
Precedence/Associativity of Arithmetic Operators
6
Example
2
1
6
5
3
7
4
x 5 6 4 - 2 6 / 3 10 3
x 5 24 - 2 6 / 3 10 3
x 5 24 - 12 / 3 10 3
x 5 24 - 4 10 3
x 5 24 - 4 1
x 29 - 4 1
x 25 1
x 26
7
Parentheses

• Parentheses can be used to change the usual
  order.
• Parts in ( ) are evaluated first.

8
Example

• Handwritten Expression

• In C (Without Parentheses)
• 6 4 / 2 4 / 4 3 2 / 2 ? 1 10
• In C (With Parentheses)
• ( (6 4) / 2 4) / (4 3 2 / (2 ? 1) )
  2

9
Integer Arithmetic

• If both operands of a binary operator are
  integers, the result is also an integer type.
• Be careful that the result is not too big
• short x
• x 3200010 // x can be 7680
• Division truncates any fractions
• 3 / 2 1 3 / 2 ? 1.5

10
Integer Arithmetic (Cont..)

• The remainder (modulus) operator
• can only be used with integer type operands
• always has an integer type result
• 14 10 4
• 3 10 3

11
Mixed Arithmetic

• Result is the higher data type used
• Higher data type takes most memory
• Floats are higher than Integers

8.3 5 / 2
8.3 5 / 2.0
2 (int)
2.5 (double)
10.3 (double)
10.8 (double)
12
Increment/Decrement Operators

• Increment uses
• value or value
• equivalent to
• value value 1
• Decrement uses --
• value-- or --value
• equivalent to
• value value - 1

13
Increment/Decrement Operators (Cont ..)

• Increment and decrement can appear as a prefix or
  a postfix
• Prefix increment/decrement
• Changes before the expression
• value or --value
• Postfix increment/decrement
• Changes after the expression
• value or value--

14
Prefix or Postfix?

• If the increment (or decrement) operator is used
  in a stand alone statement solely to add one
  (or subtract one) from a variables value, it can
  be used in either prefix or postfix form.
• If the increment (or decrement) operator is used
  in a statement with other operators, the prefix
  and postfix forms can yield different results.
• Well see how later . . .

15
Assignment

• Form of variable expression
• The expression on right is evaluated first.
• The resulting value is then stored in the memory
  location of variable on left.
• An automatic type coercion occurs after
  evaluation but before the value is stored if the
  types differ for expression and variable.
• A variable may have only one value at a time
• Associativity of allows multiples
• x y z 17 9

16
Type Conversion

• There can be two kinds of conversions of a value
  from one data type to another
• Implicit conversion (type coercion)
• Explicit (type casting)

17
Implicit conversion

• Any value may be assigned to any type of
  variable.
• Implicit (automatic) conversion happens when
  assigning values to different data types
• int someInt
• float someFloat
• someFloat 12 // 12 is converted to 12.0
• someInt 4.8 // fractional part is dropped
• Avoid implicit conversion

18
Explicit conversion

• Good programmers do not depend on implicit
  conversions
• Explicit conversion is done with a cast operation
• The cast operation consists of the desired data
  type and then, within parentheses, the expression
  to be converted
• int diameter 9
• float radius
• radius float(diameter) / 2

19
Example

• int(4.8) has value 4
• float(5) has value 5.0
• float(7/4) has value 1.0
• float(7)/float(4) has value 1.75

20
Example

• float loCost
• float hiCost
• loCost 12.342
• hiCost 12.348
• loCost float(int(loCost100.00.5))/100.0
• hiCost float(int(hiCost100.00.5))/100.0