Question: I have 2 db tables - one is including all the entries, the other one is the "blacklist" - means i want to select all values excluding the entries of table 2

```
$req = "SELECT * FROM table1 WHERE link_id != (SELECT id FROM table2)";
$stmt = $pdo->query($req);

foreach($stmt as $data) {

echo $data['link_id']."<br>";           

}

```

Can anyone help me out?

Answer: 
C99 has the `<stdbool.h>` header.
You can use a `int` with `1` equal to `true` or `0` equal to `false`

But I use this in my code at the top of the program, two constants to use the words `TRUE` and `FALSE` as if they were booleans:

```
#define FALSE 0
#define TRUE  1

```