View Compilation Error

0_0_31309317_12399.c:2:8: error: '_max' undeclared here (not in a function)
 int c1[_max], c2[_max];   
        ^
0_0_31309317_12399.c: In function 'main':
0_0_31309317_12399.c:8:8: error: 'cin' undeclared (first use in this function)
  while(cin >> nNum)
        ^
0_0_31309317_12399.c:8:8: note: each undeclared identifier is reported only once for each function it appears in
0_0_31309317_12399.c:29:3: error: 'cout' undeclared (first use in this function)
   cout << c1[nNum] << endl;
   ^
0_0_31309317_12399.c:29:23: error: 'endl' undeclared (first use in this function)
   cout << c1[nNum] << endl;
                       ^