View Compilation Error

0_0_22999545_11056.cpp: In function 'int main()':
0_0_22999545_11056.cpp:9:19: error: unable to find numeric literal operator 'operator""a'
   c=sqrt(a*a+4*b)/2a;
                   ^
0_0_22999545_11056.cpp:9:19: note: use -std=gnu++11 or -fext-numeric-literals to enable more built-in suffixes