View Compilation Error

0_0_31580958_10181.cpp: In function 'long long int qkpow(long long int, long long int)':
0_0_31580958_10181.cpp:37:10: error: 'mod' was not declared in this scope
  t=(t*t)%mod;
          ^
0_0_31580958_10181.cpp: In function 'int main()':
0_0_31580958_10181.cpp:51:20: error: 'mod' was not declared in this scope
   cout<<((((1+n)*n%mod)*qkpow(2,mod-2)-(solve(n)*n%mod)*qkpow(2,mod-2))%mod+mod)%mod;<<'\n';
                    ^
0_0_31580958_10181.cpp:51:86: error: expected primary-expression before '<<' token
   cout<<((((1+n)*n%mod)*qkpow(2,mod-2)-(solve(n)*n%mod)*qkpow(2,mod-2))%mod+mod)%mod;<<'\n';
                                                                                      ^