View Compilation Error

0_0_6154417_27409.cpp:4: error: `main' must return `int'
0_0_6154417_27409.cpp: In function `int main(...)':
0_0_6154417_27409.cpp:18: error: `abs' undeclared (first use this function)
0_0_6154417_27409.cpp:18: error: (Each undeclared identifier is reported only once for each function it appears in.)