Need help with this formula -b/2a..Please read.

I am a newbie here so please be kind. I am writing a program that will tell the user the vertex of a parabola. The formula for a parabola is y=ax^2+bx+c. To find the vertex of the parabola you use the formula -b/2a. So here is my problem, when the user enters 3 coefficients (a,b,c) such as 2 2 2 and you plug a and b into the formula you get zero but what I'm suppose to get is -1/2 or -.5. For example, plug in the numbers -(2)/2*2 the program spits out zero. The rule is 1 divided 2 is zero but when you use a calculator of course the answer is .5. How can I get around this. Please help, this is due tomorrow night.