View Compilation Error

286117_0_16687.cpp: In function `int in_dist(point_t*, point_t*)':
286117_0_16687.cpp:21: error: `abs' undeclared (first use this function)
286117_0_16687.cpp:21: error: (Each undeclared identifier is reported only once for each function it appears in.)
286117_0_16687.cpp: In function `int in_max(point_t*, int, int, int)':
286117_0_16687.cpp:36: error: `abs' undeclared (first use this function)