View Compilation Error

0_0_36785185_23450.cpp: In function 'long long int qmi(long long int, long long int)':
0_0_36785185_23450.cpp:31:35: error: 'mod' was not declared in this scope
         if(b & 1) res = res * a % mod;
                                   ^
0_0_36785185_23450.cpp:33:21: error: 'mod' was not declared in this scope
         a = a * a % mod;
                     ^