View Compilation Error

0_0_17743130_2435.cpp: In function 'int main()':
0_0_17743130_2435.cpp:7:63: error: 'sqrt' was not declared in this scope
   printf("%.2f\n",sqrt((x1 - x2)*(x1 - x2)+(y1 - y2)*(y1 - y2)));
                                                               ^