Key Considerations for const Usage:

• Variables declared with const cannot be modified
• const variables must be initialized during declaration
• When initializing one object with another, their const status doesn't affect compatibility

int value = 42;
const int const_value = value;
int new_value = const_value;

References to Constants:

• Constants (const variabels) must be bound to constant references

const int max_size = 1024;
const int& ref1 = max_size;
// int& ref2 = max_size; // Error: non-const reference to const object

Top-level vs Low-level const:

These concepts determine validity during copying (assignment or parameter passing).

Top-level const can apply to any object type (pointers, references, primitives). Low-level const only applies to compound types like pointers and references.

Idenitfying const Levels:

1. By syntax:

   • If const appears without & or * before the varible name, it's top-level
   • Otherwise, it's low-level

2. For pointers:

   • If pointer address cannot change (const pointer), it's top-level
   • If pointer points to const data, it's low-level

const int fixed = 10;
// int* ptr = &fixed; // Error: cannot convert const int* to int*

Copy Assignment Rules:

• Top-level const can be ignored during assignment
• Low-level const must match on both sides
• Non-const can convert to const, but not vice versa

int x = 0;
const int y = 42;
const int* ptr1 = &y;
ptr1 = &x; // Valid: int* converts to const int*

Reference Initialization Rules:

int num = 0;
const int& const_ref = 10;
num = const_ref; // Valid assignment

Pointer Examples:

int var1 = 10;
const int var2 = 20;
// int* const ptr2 = &var2; // Error: cannot convert const int* to int*
const int* const ptr3 = &var1; // Valid
// int* ptr4 = ptr3; // Error: cannot convert const int* to int*

Assignment Behavior:

int a = 10, b = 20;
const int c = 42;
const int* ptrA = &c;
const int* const ptrB = ptrA;
int* const ptrC = &a;

// *ptrA = *ptrB; // Error: cannot modify const data
ptrA = ptrB; // Valid: pointer value can change
// ptrC = &b; // Error: cannot change const pointer