3.2 Recursion (Eloquent JavaScript Solutions)

3-2 Eloquent Javascript Solutions.js

function isEven(num) {
  if (num == 0)
    return true;
  if (num == 1)
    return false;
  if (num < 0)
    return "??";
  else return isEven(num - 2);
}

console.log(isEven(50));
// → true
console.log(isEven(75));
// → false
console.log(isEven(-1));
// → ??

Hints

Your function will likely look somewhat similar to the inner find function in the recursive findSolution example in this chapter, with an if/else if/else chain that tests which of the three cases applies. The final else, corresponding to the third case, makes the recursive call. Each of the branches should contain a return statement or in some other way arrange for a specific value to be returned.

When given a negative number, the function will recurse again and again, passing itself an ever more negative number, thus getting further and further away from returning a result. It will eventually run out of stack space and abort.

Thanks