How to concatenate PHP variable name?

You should use ${'varname'} syntax:

for ($counter=0,$counter<=67,$counter++){
    echo $counter;
    ${'check' . $counter} ="some value";
}

this will work, but why not just use an array?

$check[$counter] = "some value";

The proper syntax for variable variables is:

${"check" . $counter} = "some value";

However, I highly discourage this. What you're trying to accomplish can most likely be solved more elegantly by using arrays. Example usage:

// Setting values
$check = array();
for ($counter = 0; $counter <= 67; $counter++){
    echo $counter;
    $check[] = "some value";
}

// Iterating through the values
foreach($check as $value) {
    echo $value;
}