#define CONSTANT - how to change it's value?

Hi,

what does this error mean and how to fix it?
'=' : left operand must be l-value

Code:

---

#include <stdio.h>
#define TAX 0.10

void main() {
        float bal, t;
        bal = (float)72.10;
        TAX = 0.20;
        t = bal * (float)TAX;
        printf("The tax on %.2f is %.2f\n", bal, t);
}

---

Thanks

You can't change a #define like that. If you want to change the value throughout your program just make it a variable ( local or global ) and then change it. When you have a #define the whole idea is that it is constant for the life of the program. You cannot modify that value.

Thanks for explanation. Yes, it is a constant and illegal to change it.

Ahh, and about your code, don't use void main(), the main() function only returns integer.

Another way to declare constants is:

Code:

---

const int blah;
const type name;

---

>Another way to declare constants is:
Not in C. Using the const keyword on a variable merely makes it read-only where if you innocently try to modify the value, you get an error. A true constant can be used as the size for an array:

Code:

---

#include <stddef.h>

#define CONSTANT 10
const size_t READONLY = 10;

int main ( void )
{
  int array1[CONSTANT]; /* Legal */
  int array2[READONLY]; /* Bzzt! Error */

  return 0;
}

---

-Prelude