How to Subtract positive and negative integers

How to subtract positive and negative integers:

There are four types of subtraction:

1)subtract positive from a positive integers

2)subtract negative from a negative

3)subtract positive from a negative

4)subtract negative from a positive

First you go to positive from positive for example you take 12-9 then

you get 3. As it is the same 9-12 you will get -3. Then you go to next negative from negative for example -12-(-9) implies -12+9=-3(as per rules),

and next, subtract positive from a negative integers. For example :-10-(9),in this -10 is a negative integer and 9 is a positive integer then you will get result -10-9=-19.

Next subtract a negative from a positive integers for example: 12-(-10) then you will get 12+10=22.