Probability of getting the particular summ of two numbers in C++

There are two cubes and different numbers from 1 to 6 on each plane surfaces of the cubes. After we throw up the cubes, we get two numbers on two of the plane surfaces. I need to create a code which would calculate the probability of getting the particular summ (which could be from 2 to 12) of those numbers on the plane surfaces. I also need to use the function "rand()". Does anyone have any ideas how to do this? Thanks in advance.