View Compilation Error

1_277_3793_252.cpp:8: error: `main' must return `int'
1_277_3793_252.cpp: In function `int main(...)':
1_277_3793_252.cpp:30: error: `abs' undeclared (first use this function)
1_277_3793_252.cpp:30: error: (Each undeclared identifier is reported only once for each function it appears in.)