View Compilation Error

0_0_15361532_19794.cpp: In function 'int main()':
0_0_15361532_19794.cpp:5:59: error: 'C' was not declared in this scope
   while (T--) { scanf("%d", &n); printf("Case #%d: %d\n", C, n * 2 - 1); }
                                                           ^