A question regarding const

[LarryChen]

Here is the code,

void foo(const char* s)
{
	s = "mary";
}

int main()
{
	char* s = "john";
	foo(s);

	cout<<s<<endl;

	return 0;
}

It compiles just fine. But if I change the definition of the function foo a little bit like this,

void foo(const char* &s)
{
	s = "mary";
}

Then I got compiler errors like "cannot convert parameter 1 from 'char *' to 'const char *&'". It looks like it is fine convert char* to const char* but it is not fine to convert char* to const char *&. Why? Thanks.