The Keyword const

Declaring an entity to be const tells the compiler to make it "read-only." const can be applied usefully in a large number of programming situations, as we will soon see.

Because it cannot be assigned to, a const object must be properly initialized. For example:

const int x = 33; const int v[] = {3, 6, x, 2 * x};

Working with the declarations above:

++x ; // error v[2] = 44; // error

Compilers can take advantage of an object being read-only in various ways. For integers and some simple types, no storage needs to be allocated for a const unless its address is taken. Therefore, most optimizing compilers try to store them in static memory.

It is good programming style to use const entities instead of embedding constant expressions (sometimes called "magic numbers") in your code. This will gain you flexibility later when you need to change the values and, in general, it will improve the maintainability of your programs. For example, instead of something like this:

for(i = 0; i < 327; ++i) { ... }

use something like this:

// const declaration section of your code const int SIZE = 327; ... for(i = 0; i < SIZE; ++i) { ... }