is_numeric
(PHP 4, PHP 5)

is_numeric -- Finds whether a variable is a number or a numeric string
Description
bool is_numeric ( mixed var )

Finds whether the given variable is numeric. Numeric strings consist of optional sign, any number of digits, optional decimal part and optional exponential part. Thus +0123.45e6 is a valid numeric value. Hexadecimal notation (0xFF) is allowed too but only without sign, decimal and exponential part.

Parameters

var
The variable being evaluated.

Return Values
Returns TRUE if var is a number or a numeric string, FALSE otherwise.

See Also

ctype_digit()
is_bool()
is_null()
is_float()
is_int()
is_string()
is_object()
is_array()

$a="a";
$b=0; //或$b=20;

if(is_numeric($b))
{
echo "Number";
}
else
{
echo "Not Number";
}

is_numeric($a);
是返回為TRUE 不是返回為FALSE