public static  int eval(string exp)
        {
            stack1 s = new stack1 (9);
            for (int i = 0; i <= exp.Length - 1;i++ )
            {
                if (exp[i] != '*' && exp[i] != '+' && exp[i] != '/' && exp[i] != '-')
                {
                   string  t = exp[i].ToString();
                    s.push(int.Parse(t));
                }

                else
                {

                    switch(exp[i])
                    {
                        case '*':
                           int  op1 = s.pop();
                            int  op2 = s.pop();
                            int res = op1 * op2;
                            s.push(res);
                            break;

                        case '+':
                            int op3 = s.pop();
                            int op4 = s.pop();
                            int res1 = op3 + op4;
                            s.push(res1);
                            break;

                        case '-':
                            int op5 = s.pop();
                            int op6 = s.pop();
                            int res2 = op6 - op5;
                            s.push(res2);
                            break;

                        case '/':
                            int op7 = s.pop();
                            int op8 = s.pop();
                            int res3 = op8 / op7;
                            s.push(res3);
                            break;


                    }
                }
            }
            return s.pop();

        }