Beginner

misseb · September 7th, 2009, 07:45 PM

I am an absolute beginner with all programming. I am currently completing a course through independent study, but am stuck and have not had a response from the instructor.

I am required to use Javascript code to calculate sales tax on 3 sales totals entered. I think I understand if else statements and loops, but I don't know how to do this referencing the constants he has given us?

SALES_LIMITS = new Array (
0, // For bracket 0
50, // 1
100, // 2
250, // 3
500, // 4
);

TAX_RATES = new Array (
0.00, // For bracket 0
0.05, // 1
0.075, // 2
0.10, // 3
0.20 // 4);

Can anyone explain how to do this to me. Please be nice I am very new at all of this.

Thanks

Em

om_prakash · September 8th, 2009, 01:22 AM

Assuming you have following requirement, You need to calculate tax as follows:
IF SALES_LIMITS is between
0-50 0.75
50-100 0.075
100-25 0.10
> 500 0.20

Code:

function Check() 
{
var salesAmt = 67; 
var taxAmt = 0; 
if(salesAmt >=0 && salesAmt <=50) { 
taxAmt = salesAmt*0.05; } 
else if(salesAmt>50 && salesAmt <=100) { 
taxAmt = salesAmt*0.075; } 
else if(salesAmt>100 && salesAmt <=250) { 
taxAmt = salesAmt*0.10; } 
else if(salesAmt>250 && salesAmt <=500) { 
taxAmt = salesAmt*0.20; } 
else { 
taxAmt = salesAmt*0.20; 
} 
salesAmt = salesAmt + taxAmt 
alert(salesAmt); }

Old Pedant · September 8th, 2009, 05:13 PM

Except this code is a bit overkill.

After all, if your IF does "... && salesAmt <= 50 ...", then there is no need to test for > 50! BY DEFINITION you wouldn't REACH the next IF unless salesAmt is > 50.

Also, if you want to make it MUCH more flexible, you SHOULD base the code on the arrays, as described in the original post. Except I'd use a "unified" array insted of two separate ones.

So:

Code:

var taxBrackets = [ [50, 0.00], [100, 0.05], [250, 0.075], [500, 0.10], [1000000000, 0.20] ];
 
function getTaxForSale( saleamt )
{
    for ( var t = 0; t < taxBrackets.length; ++t )
    {
        var bracket = taxBrackets[t];
        if ( saleamt < bracket[0] ) return bracket[1];
    }
    // should never get here, unless the sale is over 1000000000
    return 0.20; // or whatever the rate for over 1000000000 should be
}

A variation on that, so we don't have to worry about the 1000000000, even:

Code:

var taxBrackets = [ [50, 0.00], [100, 0.05], [250, 0.075], [500, 0.10], [null, 0.20] ];
 
function getTaxForSale( saleamt )
{
    for ( var t = 0; t < taxBrackets.length; ++t )
    {
        var bracket = taxBrackets[t];
        if ( bracket[0] == null || saleamt < bracket[0] ) return bracket[1];
    }
}

And, of course, if you preferred to return the tax *AMOUNT* instead of just the rate, then simply do

Code:

 
        if ( bracket[0] == null || saleamt < bracket[0] ) return saleamt * bracket[1];

instead.