/in/foo.cc: In function 'int main()':
/in/foo.cc:20:28: error: 'memset' was not declared in this scope
  memset(flag,0,sizeof(flag));
                            ^
/in/foo.cc:23:5: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
     for(int i=1;i<=n;i++)
     ^~~
/in/foo.cc:26:2: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
  for(int i=n;i>=1;i--)
  ^~~