What is wrong with this recursion function? fac(5) gives NaN
function fac(num){
while(num>2){
return(num*fac(num-1))
}
}
4 Answers
fac(1) returns nothing, which is undefined, and undefined*1 is NaN, that's why.
Change your code to
function fac(num){
return num>2 ? num*fac(num-1) : 1;
}
Comments
The correct way should be:
function fact(num) {
if(num > 2)
return num * fact(num - 1);
else
return num;
}
Comments
NaN - not a number error , occurs usually but not limited to when we try to apply a numerical operation to a value which is not a number.
The Issue at hand is when the input value is less than 2 , the function return undefined, which is not a number, so the return (num*fac(num-1)) will fail due to num * undefined.
to fix this , we have to return a value when number is 2 or less than 2.
function fact(num) {
if(num > 2)
return num * fact(num - 1);
else
return num;
}
2 Comments
Denys Séguret
Your first sentence might make people think applying a numerical operation on numbers doesn't produce NaN. Please fix it.
Akash Yadav
Thanks for pointing it out, have corrected the sentence to depict the same
What's wrong with your code
function fac(num){
while(num>2){
return(num*fac(num-1))
}
}
No return value for
num <= 2. So, at some point your code will multiplyNumberwithundefinedwhich results inNaNwhileloop is not needed
function fac(num) {
return (num > 2) ? num * fac(num - 1) : 1;
}
alert(fac(5));
num <= 2. So at some point your code will multiply thenumberwithundefined