View Compilation Error

0_0_30855265_20594.cpp: In function 'll pow_mod(ll, ll, ll)':
0_0_30855265_20594.cpp:48:6: error: 'b' was not declared in this scope
   if(b&1) res=res*a%m;
      ^
0_0_30855265_20594.cpp:50:3: error: 'b' was not declared in this scope
   b>>=1;
   ^