When we should really use constant and define

code with define keyword

Code:

---

#include <stdio.h>

#define x  20


int main(void)
{
  printf("x = %d \n", x);
 
  return 0;
}

---

x = 20

code with constant keyword

Code:

---

#include <stdio.h>

int main(void)
{
        int x = 20;
       
  printf("x = %d \n", x);
 
  return 0;
}

---

x = 20

I don't see the difference between constant and define keyword in code

somebody can explain When we should really use constant and define keyword in code ?

Use constant whenever it works.
But, use define where it does not work.

You need to use define when it is an array dimension; that is the first place that constants do not work in C that I run across on a normal daily use.

Note: There is also enum types.

EDIT: Your code does *not* use a constant!!!

Tim S.

Quote:

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Originally Posted by stahta01

EDIT: Your code does *not* use a constant!!!

Tim S.

---

My mistake

Code:

---

#include <stdio.h>
int main(void)
{
  const int x = 20;
   
  printf("x = %d \n", x);
   
  return 0;
}

---

Quote:

---

Originally Posted by stahta01

Use constant whenever it works.
But, use define where it does not work.
.

---

Thanks Tim S you gave one example of array. I have still doubt I am looking good reason to use constant / define

My question is which one should we really need ?

Best rule of thumb: if the job can be done without it, use something else. Most useful thing about a #define is conditional compilation anyway...