[php] Detecting negative numbers

I was wondering if there is any way to detect if a number is negative in PHP?

I have the following code:

$profitloss = $result->date_sold_price - $result->date_bought_price;

I need to find out if $profitloss is negative and if it is, I need to echo out that it is.

Just multiply the number by -1 and check if the result is positive.

I believe this is what you were looking for:

class Expression {
    protected $expression;
    protected $result;

    public function __construct($expression) {
        $this->expression = $expression;
    }

    public function evaluate() {
        $this->result = eval("return ".$this->expression.";");
        return $this;
    }

    public function getResult() {
        return $this->result;
    }
}

class NegativeFinder {
    protected $expressionObj;

    public function __construct(Expression $expressionObj) {
        $this->expressionObj = $expressionObj;
    }

    public function isItNegative() {
        $result = $this->expressionObj->evaluate()->getResult();

        if($this->hasMinusSign($result)) {
            return true;
        } else {
            return false;
        }
    }

    protected function hasMinusSign($value) {
        return (substr(strval($value), 0, 1) == "-");
    }
}

Usage:

$soldPrice = 1;
$boughtPrice = 2;
$negativeFinderObj = new NegativeFinder(new Expression("$soldPrice - $boughtPrice"));

echo ($negativeFinderObj->isItNegative()) ? "It is negative!" : "It is not negative :(";

Do however note that eval is a dangerous function, therefore use it only if you really, really need to find out if a number is negative.

:-)

You could check if $profitloss < 0

if ($profitloss < 0):
    echo "Less than 0\n";
endif;

if ( $profitloss < 0 ) {
   echo "negative";
};

Can be easily achieved with a ternary operator.

$is_negative = $profitloss < 0 ? true : false;

Don't get me wrong, but you can do this way ;)

function nagitive_check($value){
if (isset($value)){
    if (substr(strval($value), 0, 1) == "-"){
    return 'It is negative<br>';
} else {
    return 'It is not negative!<br>';
}
    }
}

Output:

echo nagitive_check(-100);  // It is negative
echo nagitive_check(200);  // It is not negative!
echo nagitive_check(200-300);  // It is negative
echo nagitive_check(200-300+1000);  // It is not negative!

You could use a ternary operator like this one, to make it a one liner.

echo ($profitloss < 0) ? 'false' : 'true';

if(x < 0)
if(abs(x) != x)
if(substr(strval(x), 0, 1) == "-")

I assume that the main idea is to find if number is negative and display it in correct format.

For those who use PHP5.3 might be interested in using Number Formatter Class - http://php.net/manual/en/class.numberformatter.php. This function, as well as range of other useful things, can format your number.

$profitLoss = 25000 - 55000;

$a= new \NumberFormatter("en-UK", \NumberFormatter::CURRENCY); 
$a->formatCurrency($profitLoss, 'EUR');
// would display (€30,000.00)

Here also a reference to why brackets are used for negative numbers: http://www.open.edu/openlearn/money-management/introduction-bookkeeping-and-accounting/content-section-1.7