View Compilation Error

0_0_37995504_4036.cpp:68:25: error: 'approx' function uses 'auto' type specifier without trailing return type
  auto approx(int A = 1E3) {
                         ^
0_0_37995504_4036.cpp:68:25: note: deduced return type only available with -std=c++1y or -std=gnu++1y