View Compilation Error

0_0_15450738_32348.cpp:2:11: error: '::main' must return 'int'
 void main()
           ^
0_0_15450738_32348.cpp: In function 'int main()':
0_0_15450738_32348.cpp:7:10: error: 'r4' was not declared in this scope
  s=a*r*r*r4/3;
          ^