JavaScript fails to add properly, adds as if strings are present?

tanayp5 · 10-25-2011, 11:03 PM

Sorry for my beginner question but I am having some trouble getting this to work. I am trying to create a simple I=PRT calculator so it can calculate interest. But when you run it it adds the digits. Ex. 5+100=5100 instead of 105. Give it a try. My code is bellow.[CODE]

// JavaScript Document
alert("This is a simple calculator which will allow you to calculate the interest on a principle.");

var principle = prompt("What is the amount you would like to calculate interest for?");

var rate = prompt("What is the interest rate. eg. For 3.9% write 3.9");

var term = prompt("How long in the period under calculation going to be? eg. For 1 year write 1");

var interest = principle*(rate/100)*term;

var result = principle + interest;

var a = "This means the interest is going to be $";

var b = " And the total to be paid is $";

var c = a + interest + b + result;

alert(c);

[CODE]

Thanks in advance.

jmrker · 10-26-2011, 01:04 AM

If ANY variable is a string, then the + of the intended math is treated as concatenation.

You could try:

Code:

var c = Number(a) + Number(interest) + Number(b) + (Number(principle) + Number(interest));

// or
var result = (principle*1) + (interest*1);
var c = (a*1) + (interest*1) + (b*1) + result;

// or a few other variations on the theme
// parseFloat() or parseInt() come to mind.

tanayp5 · 10-26-2011, 01:24 AM

Quote:

Originally Posted by jmrker

If ANY variable is a string, then the + of the intended math is treated as concatenation.

You could try:

Code:

var c = Number(a) + Number(interest) + Number(b) + (Number(principle) + Number(interest));

// or
var result = (principle*1) + (interest*1);
var c = (a*1) + (interest*1) + (b*1) + result;

// or a few other variations on the theme
// parseFloat() or parseInt() come to mind.

Thanks so much for your help, I got it to work right away. By the way, if possible can you please simplify what you did to help me solve the problem.