1. Lesson 4: Formatting Input Data for Arithmetic
JavaScript 101
Lesson 4: Formatting Input Data for Arithmetic

2. Lesson Topics Data types String data versus numeric data
How input data (from the prompt method) is stored as a string
Why you need to format input data for arithmetic
How to use built in JavaScript functions to format input data for arithmetic (parseInt, parseFloat, and eval)

3. Data Types
Data type is a category of information used by a programming language
Identifies the type (kind) of information a program can represent
JavaScript has three basic data types:
String
Numeric
Boolean

4. String data vs. numeric data
String data is used to input and output information
Numeric data can carry out arithmetic
All information in a computer is stored using just 0s and 1s
Inside the computer, strings and numbers use different patterns to store information
Need to change a string pattern into a number pattern before computer can execute arithmetic

5. String data versus Numeric data
When the prompt method is used to collect data from a Web page visitor, information input is a string
Information in the form of a string must be formatted as a number before it can be used for arithmetic

6. How to convert strings to numbers
Use these JavaScript methods
The parseFloat() method
The parseInt() method
The eval() method

7. The parseFloat() Method
Syntax:
var number=parseFloat(string1);
parseFloat takes the value stored in string1 and translates it to a decimal format and stores the number in the variable number

8. The parseInt() Method Syntax: var wholeNumber=parseInt(string1):
parseFloat takes the value stored in string1 and translates it to a decimal format and stores the number in the variable number

9. The eval() Method
The eval() method evaluates a numeric expression in the form of a string and returns its value
Syntax:
var result=eval(string1);
Where string1 is a numeric expression in string format

10. In the lab
Use JavaScript methods to convert user input from string format to numeric format and then carry out arithmetic operations
Open Notepad and create a new HTML document named lesson0401.html
Enter the code on p. 4-6 exactly as you see it
Save the file and open it using either Internet Explorer or Netscape

11. Student Modifications
Modify the code on p. 4-6 to prompt users to enter the age of their dog, using parseFloat(), convert the dog’s age to human years using the following formula
dogToHumanYears = ((dogAge-1) * 7) + 9
Do other conversions, from cat years (cats live about 20 years) to human years. Look on the internet for other possibilities

12. Lesson Summary Data types String data versus numeric data
Input data from the prompt method stores is a string
Data in string format cannot be used for arithmetic
JavaScript methods to convert strings into numbers
After conversion, arithmetic can be carried out

13. Lesson Summary (cont.)
The parseFloat method, which converts a string to a decimal number
The parseInt method, which converts a string to an integer
The eval method, which converts an expression in the form of a string into a numeric value