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BIT116 : Scripting

In this lesson, we will learn how to detect if user input is numeric in JavaScript. We will cover the isNaN() function, parseFloat(), and parseInt(). Practice exercises included.

johnlclark
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BIT116 : Scripting

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  1. BIT116: Scripting Checking If User Input Is Numeric

  2. Snomagedon 2019: • Part 1 • (Mon/Tues Feb 4/5) • We’re going to push the schedule forward 1 day up to the midterm • Next Tuesday was a study day, so we’re going to replace it with new material • The midterm still happens on Thursday, Feb 14th • Possible Part 2 • (Mon/Tues Feb 11/12) • If we miss class next week then we’ll push the schedule back, including the day of the midterm • I will announce the push-back on Canvas

  3. Today • Quiz • Detecting numeric input • Q+A on A1, A2, etc

  4. Upcoming • This week: • ASSIGNMENT 1 WAS DUE ON TUESDAY • I haven’t started grading it yet; you can still hand it in, penalty-free • Week after that: • Tuesday: • Radio buttons, check boxes • Exam Review, Exam Q+A time • Assignment 2 is due on this day • YOU ALL WILL GET AN EXTRA REVISION FOR ASSIGNMENT #2 • Thursday • Midterm exam • (more details on the next slides)

  5. Midterm Exam • Thurs, Feb 14th(Unless the Snowmagedon pushes it back a day) • You’ve got the entire class for the exam • You can leave when you’re done • You’re welcome to bring drinks + snacks • Please eat/drink quietly • If you spill something on a computer you’ll be paying for another one. • PLEASE BRING YOUR 3X5 CARD FILLED (BOTH SIDES) WITH HAND-WRITTEN NOTES

  6. Midterm Exam • Paper and pencil ONLY • Practice writing code in, say, NotePad • Practice writing code on paper • Memorize common patterns • “put a textbox and a button on a page, when the user clicks the button get the input and…..” • Detecting non-numeric input (today’s topic) • PLEASE BRING YOUR 3X5 CARD FILLED (BOTH SIDES) WITH HAND-WRITTEN NOTES

  7. Checking if a value is a number

  8. JavaScript is loosely typed • Examples of data types: • Integer - whole numbers only, but positive, negative, and zero are allowed • Floating-point / real - any number (whole or with a decimal point), positive, negative, zero • Strings – text ("a string of individual characters") • Boolean – true or false • JS will try to convert from one to another in order to help you out. • FILE:loose_typing.html • Note: multiplying by two is great • Adding 4 isn't great • Sometimes we need to tell it what to do

  9. How to check if a string (text) is a number • The isNaN() function will tell us if it's NOT a number • NaN = Not ANumber • parseFloat() will then convert it to a real, floating-point number with decimals • Use parseInt() if you want to drop anything after the decimal point • Then it's safe to do math on it • FILE:checking_for_numbers.html • Step 1: Convert it to a number using parseFloat/parseInt • Step 2: Check if it's actually a number using isNaN (error & exit if it isn't) • Step 3: Do the math 

  10. Exercise • Do exercise #1 for this topic • Once you've got that done, pick problems from exercise #2 to do

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