View Compilation Error

0_0_37917213_16559.cpp: In function 'll qpow(ll, ll)':
0_0_37917213_16559.cpp:7:7: error: 'mod' was not declared in this scope
  a %= mod;
       ^
0_0_37917213_16559.cpp: In function 'int main()':
0_0_37917213_16559.cpp:22:35: error: 'mod' was not declared in this scope
  int inv2 = (int)qpow(2ll, 1ll * (mod - 2));
                                   ^