[b]Adding[/b] two numbers with the same sign works just like the addition of numbers you already knew, but furthermore the result will get the same sign as the two integers.[br]If they have differen signs, then substract them and give the result the sign of the larger value of both integers.[br][br]For [b]substracting[/b] an integer you just have to change its sign and then add it to the other integer.