View Compilation Error

0_0_15369343_476.cpp: In function 'int main()':
0_0_15369343_476.cpp:25:56: error: 'sqrt' was not declared in this scope
      edge[k++] = sqrt(a[i].x * a[i].x + a[i].y * a[i].y);
                                                        ^
0_0_15369343_476.cpp:27:25: error: 'sort' was not declared in this scope
    sort(edge+1, edge+n+1);
                         ^
0_0_15369343_476.cpp:28:13: error: 'sqrt' was not declared in this scope
    if(sqrt(2) * edge[4] == edge[5])
             ^