View Compilation Error

0_0_3091793_27786.cpp:3: error: `main' must return `int'
0_0_3091793_27786.cpp: In function `int main(...)':
0_0_3091793_27786.cpp:6: error: `o' undeclared (first use this function)
0_0_3091793_27786.cpp:6: error: (Each undeclared identifier is reported only once for each function it appears in.)