What does it mean to declare a pointer as const?

 Declaring a pointer as const in C++ means that the value pointed to by the pointer cannot be modified through that pointer. In other words, the pointer points to a value that is read-only.

The syntax for declaring a pointer as const is to use the const keyword before the type name of the value pointed to by the pointer. For example:

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const int* p; // pointer to a constant integer

In this example, the pointer "p" points to a constant integer value that cannot be modified through "p". However, the pointer itself is not const and can still be reassigned to point to a different constant integer value.

Alternatively, we can declare a const pointer that points to a non-const value. In this case, the pointer itself cannot be modified to point to a different value, but the value pointed to by the pointer can be modified. For example:

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int x = 5;
int* const p = &x; // constant pointer to a non-constant integer

In this example, the pointer "p" is a constant pointer that points to the non-constant integer variable "x". The value of "x" can be modified through "p", but "p" cannot be modified to point to a different variable.

Using const pointers can help prevent accidental modification of data that should not be changed, and can also make code more self-documenting by making it clear which variables are meant to be read-only.