View Compilation Error

0_0_21767271_16055.cpp: In function 'int main()':
0_0_21767271_16055.cpp:17:22: error: 'scanf' was not declared in this scope
     scanf("%d",&cases);
                      ^
0_0_21767271_16055.cpp:25:41: error: 'PI' was not declared in this scope
                 if(P[i].y>0) P[i].angle=PI/2.0;
                                         ^
0_0_21767271_16055.cpp:26:34: error: 'PI' was not declared in this scope
                 else P[i].angle=-PI/2.0;
                                  ^
0_0_21767271_16055.cpp:28:51: error: 'atan' was not declared in this scope
             else P[i].angle=atan(P[i].y*1.0/P[i].x);
                                                   ^
0_0_21767271_16055.cpp:31:23: error: 'sort' was not declared in this scope
         sort(P,P+n,cmp);
                       ^
0_0_21767271_16055.cpp:63:34: error: 'max' was not declared in this scope
             ans=max(ans,lsum*rsum);
                                  ^
0_0_21767271_16055.cpp:65:9: error: 'cout' was not declared in this scope
         cout<<ans<<endl;
         ^
0_0_21767271_16055.cpp:65:20: error: 'endl' was not declared in this scope
         cout<<ans<<endl;
                    ^