View Compilation Error

0_0_37716442_27505.cpp: In function 'int main()':
0_0_37716442_27505.cpp:7:30: error: 'abs' was not declared in this scope
         double t=sqrt(abs(a-c)*abs(a-c)+abs(b-d)*abs(b-d))
                              ^
0_0_37716442_27505.cpp:7:58: error: 'sqrt' was not declared in this scope
         double t=sqrt(abs(a-c)*abs(a-c)+abs(b-d)*abs(b-d))
                                                          ^
0_0_37716442_27505.cpp:9:5: error: expected ',' or ';' before '}' token
     }
     ^