Operators

• This is chapter 2.3 of the book.
• An operator takes one or more value and combines them in some way to produce a new value.
  • In general, we will use operators with two different items
  • Variables
  • constants or values that are hard coded into the program.
• There are two types of constants
  • Literal constants or values that are included directly into the code.
  • Named constants, or a value that has an associated identifier.
• The assignment operator has two operands
  • On the left hand side (LHS) is a destination, which must be a variable
  • On the right hand side (RHS) is an expression
  • Syntax lhs = rhs
  • An expression is a combination of values, constant, literals, variables, operators and possible function calls such that when evaluated produce a resulting value.
  • Expression examples
    • 10
    • principal * rate * time
    • radius * cos(angle)
  • Statement example
    • age = 10
    • interest = principal * rate * time
    • x = radius * cos(angle)
  • The assignment operator
    1. Evaluates the expression on the RHS
    2. Sets the variable on the LHS equal to the new value.
  • If we model memory as a follows:
    • 
    • The expression y = 3*x + 7
    • Gets the value 4 stored in memory associated with x
    • Evaluates the RHS to 3*4 + 7 -> 19
    • Then places the 19 in the memory associated with y
    • Produces
    • 
  • Note, you must have a variable on the LHS,
    • 12 = 2*x+7
    • Is an illegal statement.
• Mathematical operators
  • +, -, and * (for multiply) work as you expect
  • / depends on the type of the expression.
  • % for integers computes the remainder.
• For strings
  • + usually means concatenation
  • "Hello" + "World" will produce "HelloWorld"
• Please remember my dear aunt sally.
  • Use () when needed to change this.
• Some languages support
  • a += b which is the same as a = a + b
  • a *= b which is the same as a = a * b
  • a++ which is the same as a = a + 1 but be careful in assignments.