该代码的答案应该是什么？“尝试找出原因”

Question

the Question i want to solve says 

“代码无法正确执行。尝试找出原因。”实际上，这是代码战中的问题

    //this is the problem they have given
    int multiply(int a, int b)
    {
        a * b;
    }

and i am not getting what i have to with it.