unity c# Mathf.FloorToInt(-0.5) returns 0 (acts like Mathf.CielToInt)

Question

Here's the script reference document for Mathf.FloorToInt As you can see, it should round -0.5 down to -1. For some reason it seems to return it as 0 when used with my calculations.

I have two versions of the same functions that work in a very similar way but give different outputs. My code will only ever submit integers between 3 and 18 to these functions.

This version acts as if it were using Mathf.CielToInt (returns 0 in a case of statRoll = 9):

    public int getBonus(int statRoll)
{
    int result = Mathf.FloorToInt((statRoll - 10) / 2);
    return result;
}

This is the version that works (returns -1 in a case of statRoll = 9):

    public int getBonus(int statRoll)
{
    float initial = statRoll - 10;
    float divided = initial / 2;
    int result = Mathf.FloorToInt(divided);
    return result;
}

Answer 1

You are getting bit by integer division. Both statRoll and 10 are int type, that makes initial actually a int.

Your first code is equivalent to

public int getBonus(int statRoll)
{
    int initial = statRoll - 10;
    int devisor = 2;
    int divided = initial / devisor;
    float castDevided = (float)divided
    int result = Mathf.FloorToInt(castDevided);
    return result;
}

When you do -1 / 2 you have two ints, this evaluates to 0 not -0.5 because the result must also be a int. The way to fix this is make one of the two values a float

public int getBonus(int statRoll)
{
    int result = Mathf.FloorToInt((statRoll - 10) / 2f); //adding f after a number makes it a float
    return result;
}

This makes the division between a int and a float which results in a float. The similar code would be

public int getBonus(int statRoll)
{
    int initial = statRoll - 10;
    float devisor = 2f;
    float divided = initial / devisor ;
    int result = Mathf.FloorToInt(divided);
    return result;
}