View Compilation Error

0_0_36180060_17978.cpp: In function 'long long int quick_mod(long long int, long long int)':
0_0_36180060_17978.cpp:7:22: error: 'mod' was not declared in this scope
   if(b&1)res = res*a%mod;
                      ^
0_0_36180060_17978.cpp:9:11: error: 'mod' was not declared in this scope
   a = a*a%mod
           ^