How did I beat the Javascript calculator?

问题

I created the following code to calculate numbers multiplied by eleven using the method I learnt in elementary school:

function multiplyby11(number) {
    var num = number + "";
    var integers = num.split('');
    var numbers = [];
    integers.forEach(function (val) {
        numbers.push(parseInt(val));
    });
    var multiply = [];
    multiply.push(numbers[0]);
    var number_length = numbers.length;
    for (var i = 1; i < number_length; ++i) {
        multiply.push(numbers[i] + numbers[i - 1])
    }
    multiply.push(numbers[number_length - 1]);

    function removeAllMultiplesOfTen() {
        var allRemoved = true;
        multiply.forEach(function (val, index) {
            if (val >= 10) {
                val -= 10;
                multiply[index - 1]++;
                multiply[index] = val;
                allRemoved = false;
            }
        });
        if (!allRemoved) {
            removeAllMultiplesOfTen();
        }
    }

    removeAllMultiplesOfTen();
    return multiply.join('');
}

If I input a number like 15487548796454858 my code returns

170363036761003438

But if I just do a plain javascript calculation of 15487548796454858 * 11 it returns:

170363036761003420

which is completely incorrect.

Am I running into some sort of number overflow in javascript, or did I miss something?

回答1:

In Javascript numbers are double precision floating point numbers.

That means that the precision is about 15 digits. As your calculation has 18 digits, only the first 15 are correct.

来源：https://stackoverflow.com/questions/20248038/how-did-i-beat-the-javascript-calculator

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