What is the difference between an uninitialized pointer and a null pointer?

Answer:

An uninitialized pointer is a pointer that points unknown memory location. The behavior of the uninitialized pointer is undefined. If you try to dereference the uninitialized pointer code behavior will undefine.

According to C standard, an integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant. The behavior of the uninitialized pointer is defined. When you try to dereference the null pointer then your code will crash.