View Compilation Error

0_0_39540078_23043.cpp: In function 'int main()':
0_0_39540078_23043.cpp:13:33: error: 'M_PI' was not declared in this scope; did you mean 'PI'?
   13 |         printf("%.3f\n",d*d*sin(M_PI*a/180)/2*n);
      |                                 ^~~~
      |                                 PI