View Compilation Error

0_0_17259387_17089.cpp: In function 'int compute_diff(Point, Point)':
0_0_17259387_17089.cpp:46:50: error: 'sqrt' was not declared in this scope
     return (int)(100 * (b.z - a.z) / sqrt(xx + yy));  
                                                  ^
0_0_17259387_17089.cpp: In function 'double dist(Point, Point)':
0_0_17259387_17089.cpp:54:29: error: 'sqrt' was not declared in this scope
     return sqrt(xx + yy + zz);  
                             ^