/in/foo.cc: In function 'long long int back(int, long long int)':
/in/foo.cc:29:21: warning: statement has no effect [-Wunused-value]
     if(c[i]==1) c[i]==0;
                 ~~~~^~~
/in/foo.cc: In function 'long long int back1(int, long long int)':
/in/foo.cc:20:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'long long int back(int, long long int)':
/in/foo.cc:33:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^