View Compilation Error

0_0_11904955_15785.cpp: In function `int main()':
0_0_11904955_15785.cpp:15: error: `abs' undeclared (first use this function)
0_0_11904955_15785.cpp:15: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_11904955_15785.cpp:15: error: `flag' undeclared (first use this function)
0_0_11904955_15785.cpp:28: error: expected `}' at end of input