The article explicitly says "For the sake of simplicity, in this series of posts, we assume that the argument is positive and we allow the function to round an

The article explicitly says "For the sake of simplicity, in this series of posts, we assume that the argument is positive and we allow the function to round any which way if the float argument is exactly in-between two integers." As a result, adding the condition float myround(float f) { if(f < 0) return -myround(-f); /* <-- the fix */ /* ... */ } suffices