View Compilation Error

0_0_32905957_11375.cpp: In function 'int main()':
0_0_32905957_11375.cpp:19:68: error: unable to find numeric literal operator 'operator""tan'
    double x1=mid/tan(pi*a[n]/180),x2=mid/tan(pi*a[n-1]/180),x3=mid/6tan(pi*a[n-2]/180);
                                                                    ^
0_0_32905957_11375.cpp:19:68: note: use -std=gnu++11 or -fext-numeric-literals to enable more built-in suffixes