View Compilation Error

0_0_8517881_20556.cpp:3: error: `main' must return `int'
0_0_8517881_20556.cpp: In function `int main(...)':
0_0_8517881_20556.cpp:10: error: `o' undeclared (first use this function)
0_0_8517881_20556.cpp:10: error: (Each undeclared identifier is reported only once for each function it appears in.)