View Compilation Error

0_0_22581472_28420.cpp: In function 'int main()':
0_0_22581472_28420.cpp:10:66: error: 'sqrt' was not declared in this scope
     printf("%.2lf\n",(double)sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
                                                                  ^