/in/foo.cc: In function 'int main()':
/in/foo.cc:16:10: warning: the address of 'int is(int)' will always evaluate as 'true' [-Waddress]
     if(is)
          ^
/in/foo.cc:19:6: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
      if(j%i==0)a[j]=!a[j];
      ^~
/in/foo.cc:20:5: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'if'
     if(a[i]) cout<<i<<" ";
     ^~