View Compilation Error

0_0_32214833_23925.cpp:8:7: error: 'pi' does not name a type
 const pi=3.1215926535;
       ^
0_0_32214833_23925.cpp: In function 'int main()':
0_0_32214833_23925.cpp:17:12: error: 'pi' was not declared in this scope
         t2=pi*r/v2;
            ^