View Compilation Error

0_0_27702306_21201.cpp: In function 'll qpow(ll, int)':
0_0_27702306_21201.cpp:11:23: error: 'mod' was not declared in this scope
             sum=sum*a%mod;
                       ^
0_0_27702306_21201.cpp:12:15: error: 'mod' was not declared in this scope
         a=a*a%mod;
               ^
0_0_27702306_21201.cpp: In function 'int main()':
0_0_27702306_21201.cpp:40:24: error: 'mod' was not declared in this scope
         sum1=qpow(2,c)%mod*qpow(2,a)%mod*( (qpow(2,d)-1)%mod*(qpow(2,b)-1)%mod+(qpow(2,d)-1-d)%mod )%mod + qpow(2,a)%mod*(qpow(2,b)-1-b)%mod*(qpow(2,c)-1)%mod;
                        ^