Subtract a day from a date

[Anon]

When I want to subtract a day from a date, and pass the date to a function that will do the subtraction and then return the new value, why does php sometimes subtract the year, instead of the day?
I say sometimes, because I have other identical functions that work perfectly. Does php not pass the data type along with the variable?

function subtract_a_day($datetoget)
{
$datetoget=($datetoget-1);
return_date($datetoget);
}

[Anon]

What format is the date in that is being passed to the function?

[Anon]

What format are you passing your dates as? Just the day in numerical format? A timestamp? A formatted string?

[Anon]

I assume that I'm passing them in date format.
$datetoget=date("Ymd");
I then call a function:
get_last_day($datetoget);

In my function:
get_last_day($datetoget)
{
$datetoget=($datetoget-1);
}
If I echo $datetoget in the function, I get this output: 2001-01-19, so that's why I assume that $datetoget is in date format. But when I subtract a day (as in my function), all I get is: 2000, not 2001-01-18, like I want.

[Anon]

2001-01-19 is getting trimmed to just 2001. You'll want to carefully parse and reassemble your numbers if you do it this way.

some alternative helpful functions may be mktime() and strtotime().