Thread: Help with variables and constants.

Hello Board,

I hope my questions isn't too silly. But I'm reading a book learn C in 21 days, it's a bit dated but a friend recommended it. I'm on day three where it focuses on variables. Although a part of it has got me very confused.

At one point, after describing the types of variables, it goes right in to initializing a variable right on the same line for instance:

int count = 0;

or

double percent = 0.01;

Easy enough I thought. Then I read on and it starts on constants, and specifically literal constants. It then says a literal constant can be expressed as:

int count = 20;

or

float tax_rate = 0.28;

The book goes on to explain that a constant is a value that cannot be changed during program execution.

But my question is this, what is the difference between those two examples? Defining a variable and defining a literal constant look EXACTLY the same!!! How does the compiler know the difference? How does the programmer know the difference!?!

The only tiny glimmer of difference I seem to be able to segment the two with is the fact that a variable would be defined outside the main() function, and a literal constant be defined inside any function. Whats stopping me from re-assigning a value to say tax_rate once I set the value?!

Whats the deal?

Thanks!

This

Code:

int count = 20;

is a variable. This:

Code:

const int count = 20;

is a constant.

Originally Posted by tabstop

This

Code:

int count = 20;

is a variable. This:

Code:

const int count = 20;

is a constant.

Thanks tabstop, the book must be wrong, or the editor was hitting the bottle because there is no const in front of any of their literal constant examples.

This puts me at ease.