Assignment: You get to create a four function calculator. You will have two text fields
for input, four buttons (one each for addition, subtraction, multiplication, and division),
four functions (one for each operation), and one text field for output. You should control
the layout of your calculator with a table.
Notice the use of the parseInt() function. It functions to force a variable to be of type
integer. If you don't use the parseInt function, then 6 + 6 will equal 66 because JavaScript
will treat the two sixes as strings to be concatenated instead of two integers to be added.
The plus sign is overloaded in JavaScript. This means that it performs two functions: Concatenation
and addition. You shouldn't need to use parseInt with multiplication, division, or subtraction
since these signs are not overloaded.