View Compilation Error

0_0_20616209_22582.cpp:8:27: error: 'b' has not been declared
 void add (long long &a ,  b) {
                           ^
0_0_20616209_22582.cpp: In function 'void add(long long int&, int)':
0_0_20616209_22582.cpp:9:10: error: 'b' was not declared in this scope
     a += b ; if (a<0) a+=mod ; if (a>=mod) a-=mod ;
          ^
0_0_20616209_22582.cpp: In constructor 'mat::mat(int, int)':
0_0_20616209_22582.cpp:16:19: error: 'i' was not declared in this scope
         memset (e[i],0,sizeof(int)*m) ;
                   ^
0_0_20616209_22582.cpp: In member function 'mat mat::operator*(const mat&)':
0_0_20616209_22582.cpp:23:35: error: invalid initialization of reference of type 'long long int&' from expression of type 'int'
                     add(ret.e[i][j],1ll*e[i][z]*rhs.e[z][j]%mod) ;
                                   ^
0_0_20616209_22582.cpp:8:6: note: in passing argument 1 of 'void add(long long int&, int)'
 void add (long long &a ,  b) {
      ^