计算Javascript中的平方和

Question

I am having issues calculating the sum of squares in javascript. I get lost when I define the for the loop and the variable index. Can anyone help me understand what i am doing wrong?

var sums = [];
var sumsqs= Number(prompt("Please enter a number to sum the square"));
for (var index = 0; index < sumsqs.length; index++) {
var total = total + sumsqs[index] * sumsqs[index];

document.write("<h1>The sum of squares is " + total + ".</h1>");

Thank you, Viv

Answer 1

If you're looking to convert, say, a comma-separated list of numbers to an array of numbers, that is not

Number(prompt("Please enter a number to sum the square"))

(which will attempt to convert the entire string to a number), but rather

prompt("Please enter a number to sum the square").split(",").map(Number)

You also can't declare and start to use total at the same time; you'll get NaN. Declare and initialize it before the loop:

var total = 0;

for (var index = 0; index < sumsqs.length; index++) {
    total += sumsqs[index] * sumsqs[index];
}

Answer 2

var inputNumber = Number(prompt("Please enter a number to sum the square"));
document.write("<h1>The sum of squares is " +
   ((inputNumber * (inputNumber + 1) * (2 * inputNumber + 1))/6) + ".</h1>");

It uses the formula mentioned here to calculate the result. http://library.thinkquest.org/20991/gather/formula/data/209.html

Answer 3

Thanks for everyone feedback. I just saw it a little too late. Here's what I did to complete the assignment. I was able to figure it out with help of web console.

Thanks again!

var sumsqs = [];
    var sumsq = Number(prompt("Please enter a number to calculate the sum the square or -1 to stop"));
    while (sumsq != -1) {
    sumsqs.push(sumsq);
      sumsq = Number(prompt("Please enter a number to calculate the sum the square or -1 to stop"));
    }

    var total_sumsqs = 0;
    for (var index = 0; index < sumsqs.length; index++) {
    total_sumsqs = total_sumsqs + sumsqs[index] * sumsqs[index];
    }

    document.write("<h3>The sum of squares is " + total_sumsqs + ".</h3>");

Answer 4

You can calculate the sum of squares of a comma-separated list using the following expression:

Math.hypot(...prompt().split`,`)**2

Explanation:

...prompt().split`,` accepts user input and creates an array from the input using , as the delimiter. Then the elements of the result array are converted to arguments for Math.hypot() using the spread operator .

Math.hypot() returns the square root of the sum of squares of its arguments, so if you raise the result to the power of 2 using the exponentiation operator , you can obtain the sum of squares.