How # flag in printf works?

Question

#include 
int main()
{
  float x;
  x=(int)(float)(double)(5.5);
  printf(\"%#u\",x);
  return 0;
}

How the # flag in the p

Answer 1

From the manual page:

#

The value should be converted to an "alternate form" [...] For other conversions, the result is undefined.

So yes, it's undefined.