How to add two strings as if they were numbers? [duplicate]

Answer 1

You may use like this:

var num1 = '20',
    num2 = '30.5';

alert((num1*1) + (num2*1)); //result 50.5

When apply *1 in num1, convert string a number.

if num1 contains a letter or a comma, returns NaN multiplying by 1

if num1 is null, num1 returns 0

kind regards!!!

Answer 2

If you need to add two strings together which are very large numbers you'll need to evaluate the addition at every string position:

function addStrings(str1, str2){
  str1a = str1.split('').reverse();
  str2a = str2.split('').reverse();
  let output = '';
  let longer = Math.max(str1.length, str2.length);
  let carry = false;
  for (let i = 0; i < longer; i++) {
    let result
    if (str1a[i] && str2a[i]) {
      result = parseInt(str1a[i]) + parseInt(str2a[i]);

    } else if (str1a[i] && !str2a[i]) {
      result = parseInt(str1a[i]);

    } else if (!str1a[i] && str2a[i]) {
      result = parseInt(str2a[i]);
    }

    if (carry) {
        result += 1;
        carry = false;
    }
    if(result >= 10) {
      carry = true;
      output += result.toString()[1];
    }else {
      output += result.toString();
    }
  }
  output = output.split('').reverse().join('');

  if(carry) {
    output = '1' + output;
  }
  return output;
}

Answer 3

You can use this to add numbers:

var x = +num1 + +num2;

Answer 4

try

var x = parseFloat(num1) + parseFloat(num2) ;

or, depending on your needs:

var x = parseInt(num1) + parseInt(num2) ;

http://www.javascripter.net/faq/convert2.htm

You might want to pick up the book Javascript: The Good Parts, by Douglas Crockford. Javascript has a rather sizeable colleciton of gotchas! This book goes a long way towards clarifying them. See also

• http://www.crockford.com/
• http://javascript.crockford.com/

and Mr. Crockford's excellent essay, Javascript: The World's Most Misunderstood Programming Language.

Answer 5

I would recommend to use the unary plus operator, to force an eventual string to be treated as number, inside parenthesis to make the code more readable like the following:

(+varname)

So, in your case it's:

var num1 = '20',
    num2 = '30.5';

var sum = (+num1) + (+num2);

// Just to test it
console.log( sum ); // 50.5

Answer 6

Make sure that you round your final answer to less than 16 decimal places for floats as java script is buggy.

For example 5 - 7.6 = -2.5999999999999996