How to get Factorial of number in JavaScript?

Question

I'm learning Java Script and there is an exercise about getting the factorial of number user has entered but for some reason I always get answer is = 1

here is my code :

<SCRIPT>
function factorial(num){

    for (n=1; n<=num; n++){

    return fact*n;
    }
}

var myNum, fact;

myNum = parseFloat(window.prompt('Enter positive integer : ',''));
fact = 1;
document.write('the factorial of the number is = '+ factorial(myNum));



</SCRIPT>

First try searching to see if this has been asked before http://stackoverflow.com/questions/3959211/fast-factorial-function-in-javascript — bhspencer, Nov 23 '15 at 18:54
Sorry for screenshot but when I tried to add actual code it got all wrong — Hussein Reda AlBehary, Nov 23 '15 at 19:12

score 5 · Accepted Answer · answered Nov 23 '15 at 18:55

5

The pictured code (please include actual code in the future, not screenshots of code) returns fact immediately:

for ( n = 1; n <= num; n++ ) {
  return fact * n;
}

since n starts at 1.

What you want is to include fact in the function, and multiply it as the loop goes along, then return:

function factorial(n) {
  var fact = 1;

  for ( n = 2; n <= num; n++ ) {
    fact = fact * n;
  }

  return fact;
}

answered Nov 23 '15 at 18:55

Paul Roub

36,322
27
84
93

I will mark this as Answer after 10min – Hussein Reda AlBehary Nov 23 '15 at 18:57
Sorry for screenshot but when I tried to add actual code it got all wrong – Hussein Reda AlBehary Nov 23 '15 at 18:58

score 0 · Answer 2 · answered Nov 23 '15 at 18:57

0

The reason this is returning 1 is because in your loop above, you return the value on the very first iteration, so n is never greater than 1.

answered Nov 23 '15 at 18:57

Joshua Dannemann

2,003
1
14
34

How to get Factorial of number in JavaScript?

2 Answers2