View Compilation Error

0_0_15422481_18680.cpp: In function 'void output(double)':
0_0_15422481_18680.cpp:26:24: error: 'M_PI' was not declared in this scope
     printf("%.2lf\n",S*M_PI);
                        ^
0_0_15422481_18680.cpp: In function 'void doit1()':
0_0_15422481_18680.cpp:40:24: error: 'M_PI' was not declared in this scope
     printf("%.2lf\n",S*M_PI);
                        ^