Why does the compiler complain about the assignment?

While compiling the following code, the compiler produces the warning:

assignment discards ‘const’ qualifier from pointer target type

#include<stdio.h>

int main(void)
{
 char * cp;
 const char *ccp;
 cp = ccp;
}

And this code is ok(no warning).Why?

#include<stdio.h>

int main(void)
{
 char * cp;
 const char *ccp;
 ccp = cp;
}

Edit: Then why isn't this ok?

int foo(const char **p) 
{ 
  // blah blah blah ...
}

int main(int argc, char **argv)
{
 foo(argv);
}