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Constants

Constants are defined using the define() function
  • may only evaluate to scalar type values (e.g. int,float,string)
  • have case-senstive names; written without dollar sign ($)
  • are always available globally (like super-globals)
  • may not be redefined or undefined once they have been set 

define("CONSTANT", "Hello world.");
define("MaxLevel", 6);
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and gives error
if ($i > MaxLevel) { echo "Yes"; }