Javascript For Loop alternative to setting initial variable to 1?

Question

I've made a javascript that will give the factorial of all numbers inputted into the array (minus the first number in the array "0" which I had to put there for filler purposes to make the code run correctly)

fact = [0, 4, 2, 5, 3];
factorial = 1;
for (x = 1; x < fact.length; x++) {
for (i = 1; i <= fact[x]; i++) {
 factorial *= i;
 if (fact[x] === i) {
    console.log(fact[x] + "!" + " " + "=" + " " + factorial);
     factorial = 1;
   }
  }
 }``

Everything works correctly here is the console.log:

4! = 24

2! = 2

5! = 120

3! = 6

My question is how can I change variable x and i's initial value to 0 so I can remove my space holder "0" in my array without making everything outputted to 0 because currently if i set my variables to 0 to start and remove the space holder "0" in my array the equation becomes:

factorial *= 0;

which will make everything equal to zero and I don't want that! I am very sorry I am bad at wording my question thanks for the help!

Travis J · Accepted Answer · 2013-10-24 02:32:55Z

3

jsFiddle Demo

You could replace the inner for loop with a while loop like this:

var fact = [4, 2, 5, 3];
for (x = 0; x < fact.length; x++) {
 var factorial = fact[x];
 var result = 1;
 while( factorial > 0 ){
  result *= factorial--;        
 }
 console.log(fact[x] + "!" + " " + "=" + " " + result);
}

answered Oct 24, 2013 at 2:32

Travis J

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Comments

Todd · Accepted Answer · 2013-10-24 02:48:58Z

1

Another way to do this would be to put your loop in reverse:

for (i = n; i > 0; i--) {
    fact *= i;
}

This avoids the issue with 0 in the loop. You start at the number and go backwards until you hit 1.

You could also simplify things a bit by splitting up your factorial generator function from the loop through your array:

function each (a, f) {
    var i = 0,
        r = [];

    for (i = 0; i < a.length; i++) {
        r.push(f(a[i]));
    }

    return r;
}

function factorial (n) {
    var i = 0,
        fact = 1;

    for (i = n; i > 0; i--) {
        fact *= i;
    }

    return fact;
}

var factorials = each([4, 2, 5, 3], factorial);

console.log(factorials.join(', '));

EDIT:

Fiddle here: http://jsfiddle.net/ToddT/Jy5Lp/

answered Oct 24, 2013 at 2:48

Todd

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1 Comment

Matthew Lock Over a year ago

Nice. You can reuse factorial then in a library of functions for the next project

slebetman · Accepted Answer · 2013-10-24 03:40:01Z

0

My question is how can I change variable x and i's initial value to 0 so I can remove my space holder "0"

Why would you change i to 0? It's got nothing to do with the fact array at all. Your worry is misplaced. Your code should work just fine if you remove the place holder 0:

fact = [4, 2, 5, 3];
factorial = 1;
for (x = 0; x < fact.length; x++) {
  for (i = 1; i <= fact[x]; i++) {
    factorial *= i;
    if (fact[x] === i) {
      console.log(fact[x] + "!" + " " + "=" + " " + factorial);
      factorial = 1;
    }
  }
}

answered Oct 24, 2013 at 3:40

slebetman

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