View Compilation Error

0_0_18269969_15093.cpp: In function 'void pra()':
0_0_18269969_15093.cpp:11:30: error: 'cas' was not declared in this scope
     printf("Case #%d: YES\n",cas++);
                              ^
0_0_18269969_15093.cpp: In function 'void prb()':
0_0_18269969_15093.cpp:15:29: error: 'cas' was not declared in this scope
     printf("Case #%d: NO\n",cas++);
                             ^