View Compilation Error

0_0_29283755_8856.cpp:1:2: error: 'string' does not name a type
  string str = Console.ReadLine();//获取用户输入
  ^
0_0_29283755_8856.cpp:4:9: error: expected unqualified-id before 'for'
         for (int i = 0; i <= str.Length/2; i++)
         ^
0_0_29283755_8856.cpp:4:25: error: 'i' does not name a type
         for (int i = 0; i <= str.Length/2; i++)
                         ^
0_0_29283755_8856.cpp:4:44: error: 'i' does not name a type
         for (int i = 0; i <= str.Length/2; i++)
                                            ^
0_0_29283755_8856.cpp:13:9: error: expected unqualified-id before 'if'
         if (flag == true)
         ^
0_0_29283755_8856.cpp:17:9: error: expected unqualified-id before 'else'
         else
         ^