php man page for is_numeric

IS_NUMERIC(3)								 1							     IS_NUMERIC(3)

is_numeric - Finds whether a variable is a number or a numeric string

SYNOPSIS
       bool is_numeric (mixed  $var)

DESCRIPTION
	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 (e.g.  0xf4c3b00c), Binary  (e.g.   0b10100111001),  Octal
       (e.g.  0777) notation is allowed too but only without sign, decimal and exponential part.

PARAMETERS
	      o $var
		- The variable being evaluated.

RETURN VALUES
	Returns TRUE if $var is a number or a numeric string, FALSE otherwise.

EXAMPLES
       Example #1

	      is_numeric(3) examples

	      <?php
	      $tests = array(
		  "42",
		  1337,
		  0x539,
		  02471,
		  0b10100111001,
		  1337e0,
		  "not numeric",
		  array(),
		  9.1
	      );

	      foreach ($tests as $element) {
		  if (is_numeric($element)) {
		      echo "'{$element}' is numeric", PHP_EOL;
		  } else {
		      echo "'{$element}' is NOT numeric", PHP_EOL;
		  }
	      }
	      ?>

	      The above example will output:

SEE ALSO
       ctype_digit(3), is_bool(3), is_null(3), is_float(3), is_int(3), is_string(3), is_object(3), is_array(3).

PHP Documentation Group 													     IS_NUMERIC(3)