string str = "AA+BC-CD*FI+AC/AK";
            string[] arr = str.Split(new char[] { '+', '-', '*', '/' });
            for (int i = 0; i < 100; i++)
            {
                str = string.Join(i.ToString(), arr)+i.ToString();
            }

------解决方案--------------------

放在循环里
C# code

tempStr = @"AA+BC-CD*FI+AC/AK";
                string pattern = @"(?=[+\-*/]|$)";
                string result = Regex.Replace(tempStr, pattern, "1");//AA1+BC1-CD1*FI1+AC1/AK1