View Compilation Error

0_0_18307476_22211.cpp:2:20: error: '::main' must return 'int'
 unsigned long main()
                    ^
0_0_18307476_22211.cpp: In function 'int main()':
0_0_18307476_22211.cpp:9:5: error: return-statement with no value, in function returning 'int' [-fpermissive]
     return;
     ^