View Compilation Error

0_0_6832455_24177.cpp: In function `int cmp(node, node)':
0_0_6832455_24177.cpp:27: error: `fabs' undeclared (first use this function)
0_0_6832455_24177.cpp:27: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_6832455_24177.cpp: In function `int main()':
0_0_6832455_24177.cpp:92: error: `fabs' undeclared (first use this function)