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JavaScript 101 Lesson 4: Formatting Input Data for Arithmetic

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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)

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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

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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

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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

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

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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

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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

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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

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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

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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

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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

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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

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