This code have some kind of error. It does not add numbers. Just display them without adding them. Can somebody explain why?

Question

function bankAccounts(name, coin)
{

name = prompt("Name, please");

var a = prompt("On your first account you have ", '');

var b = prompt("and on another you have ", "");

coin = a + b;

alert( "So " + name + " in total, you have " + coin + " coins.");

}

bankAccounts()

Answer 1

prompt() returns a string you have to turn it into an int or float e.g.
var a = parseInt(prompt("On your first account you have"));
Same with string -> float but parseFloat()

Answer 2

Thanks! I have to learn a lot, there are more commands then I thought.