how to declare constants

A constant, some object which you cannot modify. This is a very important feature of practically all languages. The technical representation of constants of constants is application-dependent. Parameters of functions can be constant as well.

When it comes to pointers, you need to know the difference between the following cases:

const char* constantString = "My constant string";
constantString++; //can do this
// cannot change the content of the string,
// next line won't compile:
//contstantString[0] = 'a';

char* const constantPointer = "My constant pointer";
constantPointer[0] = '!'; //can do this
// cannot modify pointer,
// next line won't compile:
//constantPointer++;

//cannot modify content or pointer:
const char* const readOnly = "Don't touch!";

If there something else you need to get explained?

—SA

to understand this you need to understand the difference between
1. pointer to constant
2. constant pointer.

1. pointer to constant

int n1 = 10;
int* pn = &n1;

suppose the address of n1 is 0x1001.
when we say pn, it is equal to 0x1001. when we say, *pn it is equal to 10;
see the below

int n1 = 10;
const int* pn = &n1;

this is a pointer to a constant integer.
means the pointer is not constant. but to what it points to is a constant;

*pn = 10; // will cause an error in this case. because we are trying to change the value of what pn is pointing to.

int n2 = 20;
pn = &n2; /* This will not cause any errors. becuse we are changing the pointer value. pn is pointing to n2 instead of n1.No problem at all*/

2. constant pointer
is the other way round of above

int n1 = 10;
int* const pn = &n1;
*pn = 10; // No error

int n2 = 20;
pn = &n2; // will cause an error

keeping all the above in mind we can say
const char* const authoeName = "Scott Meyers" /* is a constant pointer to a constant character. both the pointer and what it points to is constant.*/

const char* const authoeName = "Scott Meyers";
char* bookname = "Effective c++";

authoeName = bookname; // Error
*authoeName = *bookname; // Error

both kind of alteration will cause an error