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int main()
{
  /* Values */
            int i = 4;  // not constant, can be modified: 
                i = 5;
 
     const int ci = 6;  // constant, must be initialized
               ci = 7;  // syntax error, cannot be modified
 
  /* References */
         int &ir1 = i;  // reference, must be initialized
              ir1 = 6;
 
         int &ir2 = ci; // syntax error, const correctness would be flawed
 
  const int &cir1 = ci; // constant reference to a constant value
             cir1 = 7;  // syntax error
 
  const int &cir2 = i;  // const reference to a non-const value, still ok
             cir2 = 7;  // syntax error, cir2 is const reference
 
  /* Pointers */
         int *ip;
              ip = &i;
             *ip = 5;   // ok
 
              ip = &ci; // syntax error, const correctness would be flawed
 
  const int *cip = &ci; // ok 
            *cip = 7;   // syntax error
 
 
              ip = cip; // syntax error, C++ keeps constness
             cip = ip;  // ok, but now:
            *cip = 5;   // syntax error, wherever cip points is const 
 
  int const *icp;       // same as const int *
             icp = &i;  // ok, can assign to, icp is NOT const, *icp IS
            *icp = 5;   // syntax error, wherever icp points is const
 
  /* Can a pointer be constant? */
         int * const ipc = &i;  // ipc IS const, must be initialized         
                    *ipc = 5;   // OK, where ipc points to is NOT a const
 
        int * const ipc2 = &ci; // syntax error, ipc2 is NOT pointer to const
  const int * const cipc = &ci; // const pointer to a const
 
  return 0;
}

prog.cpp: In function 'int main()':
prog.cpp:8:19: error: assignment of read-only variable 'ci'
                ci = 7;  // syntax error, cannot be modified
                   ^
prog.cpp:14:21: error: invalid initialization of reference of type 'int&' from expression of type 'const int'
          int &ir2 = ci; // syntax error, const correctness would be flawed
                     ^
prog.cpp:17:19: error: assignment of read-only reference 'cir1'
              cir1 = 7;  // syntax error
                   ^
prog.cpp:20:19: error: assignment of read-only reference 'cir2'
              cir2 = 7;  // syntax error, cir2 is const reference
                   ^
prog.cpp:27:18: error: invalid conversion from 'const int*' to 'int*' [-fpermissive]
               ip = &ci; // syntax error, const correctness would be flawed
                  ^
prog.cpp:30:18: error: assignment of read-only location '* cip'
             *cip = 7;   // syntax error
                  ^
prog.cpp:33:18: error: invalid conversion from 'const int*' to 'int*' [-fpermissive]
               ip = cip; // syntax error, C++ keeps constness
                  ^
prog.cpp:35:18: error: assignment of read-only location '* cip'
             *cip = 5;   // syntax error, wherever cip points is const 
                  ^
prog.cpp:39:18: error: assignment of read-only location '* icp'
             *icp = 5;   // syntax error, wherever icp points is const
                  ^
prog.cpp:45:29: error: invalid conversion from 'const int*' to 'int*' [-fpermissive]
         int * const ipc2 = &ci; // syntax error, ipc2 is NOT pointer to const
                             ^

Standard output is empty