View Compilation Error

0_0_37232968_11500.cpp: In function 'int main()':
0_0_37232968_11500.cpp:2:12: error: 'PI' was not declared in this scope
 #define PI PI 3.1415927
            ^
0_0_37232968_11500.cpp:7:16: note: in expansion of macro 'PI'
   volume = 4 * PI*r*r*r / 3;
                ^