Arithemetic

• Unary operators
  • Unary operators operate on a single item (constant, variable, ...)
  • We will look at two (-,+)
  • - will flip the value of a number

    int x = 7;
    x = -x;
    cout << "x is " << x << endl;
    x = -x;
    cout << "x is " << x << endl;
    
    Will produce
    x is -7
    x is 7
           

  • + will really do nothing.

    int x = -7;
    x = +x;
    cout << "x is " << x << endl;
    
    Will produce
    x is -7
           

• Binary operators
  • Binary operators work on two operands.
  • We will look at 5.
  • +
    • Adds the two operands and resturs the sum
  • -
    • subtracts the operand on the right from the operand on the left and returns the difference.
  • *
    • Multiply the the two operand and return the product
  • /
    • Divide the left hand operand by the right hand operand.
    • / returns the something of the same type as the operands.
    • So 5/2 will return an integer (2)
    • and 5.0/2.0 will return a float (2.5)
    • This sometimes causes strange results.
  • % (the modulo operator)
    • This is only valid for integers.
    • It is the remainder (from fourth grade math division problems)
    • 5 % 3 = 2
    • 4 % 3 = 1
    • 3 % 3 = 0
    • 2 % 3 = 2
    • modulo is useful for converting units.

      If I have 207 pennies, how many pennies would I have left if I traded 
      as many as I could in for dimes.
      
              207 % 10 = 7
      	207 / 10 = 20
      
      I wouild have 20 dimes and 7 pennies.
      	    

• Increment and Decrement
  • We perform i = i + 1 often.
  • i++ is a shortcut, it is the same as i = i + 1;
  • ++i is also the same.
  • There can be problems when it is used as part of another statement.
  • i++ is a post increment, the value of i is used then it is incremented.

           i = 3;
           cout << i++;
           

  • Will produce a 3 but

           i = 3;
           cout << ++i;
           

  • Will produce a 4. I will have the value of 4 in any case.
  • i-- and --i are also available.
• A shortcut
  • We also do a = a + b; often
  • a += b; is equivelent.
  • This is true for most other operators as well.
  • a -= b; is the same as a = a - b;
• Write code to convert from Temprature in Celsius to Fahrenheight. F = C*9/5+32, C = 5/9(F-32)
• Complex Arithemetic Expressions
  • Order of operations
    • Uniary +/-
    • Multiply and Divide and Mod left to right
    • Add and subtract left to right
  • Or more fully in appendix A, page 1012
  • Order can be changed with parenthesis ()
  • Baily's rule of (), Use Em!
  • This is really just like you know how to do with math.
• Rewrite the code from above.