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JavaScript JavaScript Loops, Arrays and Objects Simplify Repetitive Tasks with Loops For Loops

Posted by David Bison
David Bison
2,838 Points

Please help me understand how the for loop is working within this function.

Hello,

I am working on a for loop within a function, and I'm having trouble understanding why it returns a value of 1 at a certain point. Here is the code I'm working with:

function firstFactorial (num) { var factorial = num; for (var i = num - 1; i > 0; i--) { factorial = factorial * i; } return factorial; }

When I pass firstFactorial the number 1, it returns a value of 1. I am under the impression that firstFactorial(1) should return the value 0.

Specifically, inside the for loop, i = num - 1. Which means i should equal 0 when num is 1.

If you could help me with this, I would be very thankful.

1 Answer

Damien Watson
Damien Watson
27,419 Points
Damien Watson
Damien Watson
27,419 Points

Hey David,

At the start, you set 'factorial = num', which means factorial is set to '1'. The for loop doesn't run because 'i' is set to '1-1' which equals '0' and the loop only runs if 'i' is > '0'.

Therefore factorial is still set to the original value of '1'. 

function firstFactorial (num) {
  var factorial = num;
  for (var i = num - 1; i > 0; i--) {
    factorial = factorial * i;
  }
  return factorial;
}
Damien Watson
Damien Watson
27,419 Points
Damien Watson
Damien Watson
27,419 Points

A further thought here, a factorial of '1' should return '1'. Because there is '1' way to organise '1'. An interesting fact is that a factorial of '0' should also return '1'.

Maybe prior to the return function, you should check if factorial is = '0' and change to '1'.

David Bison
David Bison
2,838 Points

Thank you, Damien, for the help. The suggestion for an if statement at the end is an excellent idea.