View Compilation Error

0_0_34406251_8354.cpp: In member function 'void BIT::init(int)':
0_0_34406251_8354.cpp:85:22: error: 'a' was not declared in this scope
   repi(i,1,n){ c[i]+=a[i]; int j=i+lowbit(i); if(j<=n) c[j]+=c[i]; }
                      ^