!!!Constant Expression (From MSDN)

C++ requires constant expressions — expressions that evaluate to a constant — for declarations of:

• Array bounds

• Selectors in case statements

• Bit-field length specification

• Enumeration initializers

The only operands that are legal in constant expressions are:

• Literals

• Enumeration constants

• Values declared as const that are initialized with constant expressions

• sizeof expressions

Nonintegral constants must be converted (either explicitly or implicitly) to integral types to be legal in a constant expression. Therefore, the following code is legal:

const double Size = 11.0;
char chArray[(int)Size];

From:  http://msdn.microsoft.com/en-us/library/3ffb821x.aspx

So we don't need to have constant expression when initialize a const variable:

int i = -1;
const int ic = i;        //legal.