View Compilation Error

0_0_38400733_5194.cpp: In function 'int main()':
0_0_38400733_5194.cpp:49:23: error: 'cmp' was not declared in this scope
         sort (a,a+3*n,cmp);
                       ^
0_0_38400733_5194.cpp:51:26: error: 'PIII' has no member named 'idx'
             cout<<a[i*3].idx<<' '<<a[i*3+1].idx<<' '<<a[i*3+2].idx<<'\n';
                          ^
0_0_38400733_5194.cpp:51:45: error: 'PIII' has no member named 'idx'
             cout<<a[i*3].idx<<' '<<a[i*3+1].idx<<' '<<a[i*3+2].idx<<'\n';
                                             ^
0_0_38400733_5194.cpp:51:64: error: 'PIII' has no member named 'idx'
             cout<<a[i*3].idx<<' '<<a[i*3+1].idx<<' '<<a[i*3+2].idx<<'\n';
                                                                ^