布林值 true/false 和字串 'true'/'false&

Booleans are used to represent the concepts of true and false. They are most often used for testing if a statement is true or false and they'll play a bigger role when we discuss logical expressions.Note that there is a difference between boolean true/false and the strings "true"/"false".

		Booleans and NULL


					/*	Booleans are used to represent the concepts of true and false.
				They are most often used for testing if a statement is true or false and
				they'll play a bigger role when we discuss logical expressions.
				Note that there is a difference between
					boolean true/false and the strings "true"/"false".
			*/
			$bool1 = true;
			$bool2 = false;

			// When booleans are displayed, PHP will attempt to convert them into a string
			// You'll get either "1"/"0" or "1"/"" instead of true/false
		?>
		$bool1:
		$bool2:

					/*	NULL is used to represent the concept of nothing or the state of being empty
				In the below example three variable have been set,
					then boolean tests are performed and the results are output as a string
			*/
			$var1 = 3;
			$var2 = "cat";
			$var4 = NULL;

			// isset tests whether a variable has been set
			// It returns true or false as a result of the test.
		?>
		$var1 is set:
		$var2 is set:
		$var3 is set:

		$var1 is set:
		$var2 is set:
		$var3 is set:


		$var1 empty:
		$var4 empty: