View Compilation Error

0_0_3221497_5772.cpp:4: error: `main' must return `int'
0_0_3221497_5772.cpp: In function `int main(...)':
0_0_3221497_5772.cpp:7: error: return-statement with no value, in function returning 'int'
0_0_3221497_5772.cpp:12: error: `abs' undeclared (first use this function)
0_0_3221497_5772.cpp:12: error: (Each undeclared identifier is reported only once for each function it appears in.)