View Compilation Error

0_0_38349526_17907.cpp: In function 'int main()':
0_0_38349526_17907.cpp:27:11: error: 'mod' was not declared in this scope
    res=(a%mod+(n-1)*(b-a)%mod)%mod;
           ^
0_0_38349526_17907.cpp:27:16: error: 'n' was not declared in this scope
    res=(a%mod+(n-1)*(b-a)%mod)%mod;
                ^
0_0_38349526_17907.cpp:31:26: error: 'fastpow' was not declared in this scope
    res=(a*fastpow(b/a,k-1))%mod;//注意这里要乘一个首项。
                          ^
0_0_38349526_17907.cpp:31:29: error: 'mod' was not declared in this scope
    res=(a*fastpow(b/a,k-1))%mod;//注意这里要乘一个首项。
                             ^