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  1. #1
    New to the CF scene
    Join Date
    Apr 2013
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    multiple condition while loop


    Trying to create a multiple condition while loop this is what i have:

    		<title> fuel </title>
    				var capacity = parseInt(prompt("Enter amount of gallons:",100));
    				var mpg = parseInt(prompt("Enter mpg:",100));
    				var price = parseFloat(prompt("Enter price of a gallon of petrol:"));
    				while (((capacity <=6 && capacity <=20) mpg <=20 && mpg <=75) price < 3.20 && 4.20) {
    					var eco = capacity * mpg;
    					var cost = (100 / mpg * price);
    					document.write("The car will travel: "+ eco + " : " + "the cost of travel is : " + cost);
    					mpg = 0;
    					price = 0;
    					capacity = 0;
    not sure where ive gone wrong as i haven't done one before,
    the conditions are that: gallons must be between 6 and 20
    efficiency must be between 20 and 75
    price must be between 3.20 and 4.20

    Any help would be appreciated


  • #2
    Supreme Master coder! Philip M's Avatar
    Join Date
    Jun 2002
    London, England
    Thanked 2,508 Times in 2,486 Posts
    Sounds like homework!

    A while loop is used to do a calculation repeatedly so long as some condition is true. You want to do the calculation once only. So you need to use an if statement.

    But why these conditions? If there are some limits to gallons, efficiency and price you should check that the values entered fall into the acceptable range at the time the user enters them. Not at the time the calculation is being performed. What happens if the user enters out-of-range values, or NaN entries?

    To answer your question, yes, you may have multiple conditions for a while statement. Use && to define the conditions.

    <script type = "text/javascript">
    var a = 3;
    var b = 6;
    while ((a<=10) && (b <=10)) {
    document.write((a*b) + "<br>");
    // Results:- 18 28 40 54 70
    If you want to use a while loop to ensure that a valid number is entered:-

    <script type = "text/javascript">
    var repeat = true;
    while(repeat) {
    var ans = Number(prompt("Enter a positive number max.100",""));  // use Math.floor() if an integer number is required.
    if ((isNaN(ans)) || (ans == null) || (ans < 0) || (ans > 100)) {
    alert ("You must enter a positive number max. 100");
    else {
    repeat = false;
    Be aware that prompts and document.write() are long obsolete and should only be used for testing or demonstration purposes.. Ask your teacher to update his knowledge of Javascript into the 21st Century.

    Rather than parseInt() which is intended to convert numbers fom one base to another, use Math.floor(). And prefer to use use Number() in place of parseFloat().

    “A man ceases to be a beginner in any given science and becomes a master in that science when he has
    learned that he is going to be a beginner all his life.” Robin G. Collingwood (English Philosopher, 1889-1943)
    Last edited by Philip M; 04-17-2013 at 07:02 PM.

    All the code given in this post has been tested and is intended to address the question asked.
    Unless stated otherwise it is not just a demonstration.


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