View Compilation Error

0_0_36450824_22161.cpp: In function 'll qpow(ll, ll)':
0_0_36450824_22161.cpp:26:21: error: 'mod' was not declared in this scope
   if(b&1) (res*=a)%=mod;
                     ^
0_0_36450824_22161.cpp:27:11: error: 'mod' was not declared in this scope
   (a*=a)%=mod;
           ^