This means that the compiler's never seen the variable e before. You have to declare it first, and initalize it for it to be any good.
Can you tell me how to write it? I tried it, but it is wrong. The line you wrote previously was correct. But you have to declare a variable first: int e = 0; In the above example, I created 'e' and initalized it with 0. Thus, pow(e, 3) will result in a 0.