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Title: JavaScript%20101


1
JavaScript 101
  • Lesson 3 Variables and Arithmetic

2
Lesson Topics
  • Use the arithmetic operators , -, , / to solve
    problems
  • Use the assignment operator() to give a numeric
    value to a variable
  • How operator precedence controls the order in
    which an expression is calculated
  • Use the alert method to display information
  • Use the Math object in calculations

3
Using Arithmetic Operators
  • Arithmetic operations in JavaScript are carried
    out with arithmetic symbols
  • Same as math class (except multiplication is
    rather than x)
  • These symbols are called arithmetic operators

4
Arithmetic Operators(cont.)
  • The addition operator
  • A B yields the sum of A plus B
  • The subtraction operator
  • A - B yields the difference A minus B
  • The multiplication operator
  • A B yields the product A multiplied by B
  • The division operator /
  • A / B yields the dividend of A divided by B

5
Expressions
  • Expression is computer science term for formula
  • Expression in JavaScript can combine variables,
    numbers, and arithmetic operators
  • Example var num1 6
  • var num2 3
  • num1 2 is an expression that yields 12
  • num1/num2 is an expression that yields 2

6
Assignment Operator and Expressions
  • Expressions used with the assignment operator
    give a value to a variable
  • var length 5
  • var width 6
  • var area length width (area now has a
    value of 30)

7
Expressions can combine arithmetic operators
  • Expressions can also have more than one operator
  • var length 5
  • var width 6
  • var perimeter
  • perimeter length2 width 2
  • Perimeter now has a value of 22

8
Multiple operators
  • The computer can only execute one operation at a
    time
  • When an expression has more than one operator,
    they have to be carried out in order determined
    by rule of mathematics known as operator
    precedence

9
Operator precedence
  • The operator precedence rules determine the order
    of evaluation
  • Next slide summarizes operator precedence
  • Operations are carried out in order from top to
    bottom

10
Operator Precedence Table

Type of Operator Example of Operators
Parentheses(Overrides others) ( )
Multiplication, Division , /
Addition, Subtraction , -
Assignment
11
The alert Method
  • The alert method is used to display a small pop
    up window
  • See example on p. 3-5
  • Syntax
  • alert(message)

12
In the lab
  • This lab uses arithmetic operators and alert
    statement
  • Open Notepad and create a new HTML document named
    lesson0301.html
  • Enter the code on p. 3-6 exactly as you see it
  • Add code to calculate perimeter and display its
    value with alert statement (p. 3-8)

13
Student Modifications
  • Change the first document.write statement to an
    alert statement
  • Add the following variables base, height and
    triangleArea
  • Use assignment operator to store values in base
    and height
  • Calculate and display the area of a triangle
    (formula is ½baseheight)

14
Student Modifications cont.
  • Add variables radius, circleArea,
    circleCircumference
  • Use assignment operator to assign value to radius
  • Calculate and display the area and circumference
    of a circle using the Math.PI
  • Math.PI is a defined constant that is part of
    Math object
  • Math.PI stores the value of PI

15
Lesson Summary
  • Arithmetic operators
  • Operator precedence
  • Using the alert method
  • Using the Math object
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