What are some common pitfalls or issues to watch out for when transitioning from PHP 5.6 to PHP 7.0?

// Before
$connection = mysql_connect($host, $username, $password);

// After
$connection = mysqli_connect($host, $username, $password);
```

Issue: Another common issue is the change in error handling in PHP 7.0. The mysql functions used to return false on failure, but now they throw exceptions. To fix this, you should update your error handling to catch exceptions.

```php
// Before
$result = mysql_query($query) or die(mysql_error());

// After
$result = mysqli_query($connection, $query);
if (!$result) {
    throw new Exception(mysqli_error($connection));
}
```

Issue: PHP 7.0 introduced scalar type declarations, which can cause issues if your code relies on weak typing. To address this, you can update your function declarations to specify the expected types.

```php
// Before
function add($a, $b) {
    return $a + $b;
}

// After
function add(int $a, int $b): int {
    return $a + $b;
}