View Compilation Error

0_0_36883668_7162.cpp:5:7: error: 'PI' does not name a type
 const PI = 3.1415926 ;
       ^
0_0_36883668_7162.cpp: In function 'int main()':
0_0_36883668_7162.cpp:24:30: error: 'PI' was not declared in this scope
      double bit = (0.5*log(2*PI*n)+n*log((double)n)-n)/log((double)10);
                              ^