/in/foo.cc: In function 'int main()':
/in/foo.cc:20:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int len=2;len<=n;len++)
  ^~~
/in/foo.cc:28:4: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
    cout<<f[1][n]<<endl;
    ^~~~
/in/foo.cc:9:8: warning: unused variable 'len' [-Wunused-variable]
  int n,len;
        ^~~