View Compilation Error

0_0_20943920_13449.cpp: In function 'int main()':
0_0_20943920_13449.cpp:7:8: error: 'pi' does not name a type
  const pi = acos(-1.0);
        ^
0_0_20943920_13449.cpp:9:96: error: 'pi' was not declared in this scope
   cout << setiosflags(ios::fixed) << setprecision(3) << 4.0 / 3.0 * radius * radius * radius * pi << endl;
                                                                                                ^