PHP Developer’s Dictionary IT-SC book 65 must appear on only one line and after the // indicator. Here is a quick example of using this method of commenting: // C, Java, and JavaScript programmers should understand how this method works // in the PHP programming language. /* */ Syntax /* comment */ Description The /* */ PHP element is another method of defining a comment in the PHP language. This method enables you to write comments that span multiple lines, so you can format your comments without using multiple // instances. Be careful when using this syntax and avoid nesting any comments. Here is a quick example of using this method of commenting: /* Title: Understanding comments Description: In your comments you may wish to have comments that span more than one line. If so, this is the method you should use. */ # Syntax # comment Description The # PHP element, which is commonly referred to as a "UNIX shell-style comment," enables programmers to include one-line comments in their code. This particular style is the same as the one seen in UNIX shells and, likewise, comment must appear on only one line and after the # indicator. Here is a quick example of using this method of commenting: PHP Developer’s Dictionary IT-SC book 66 # You Perl programmers should understand how this method works # in the PHP programming language. Constants Constants are a way for a programmer to define constant values for variables by using the define() method at runtime. The difference between these variables and other variables that you might have in your code is that these cannot be changed. In this section of the book, we look at several predefined PHP constants that reflect the environment in which the PHP interpreter is running. __FILE__ Syntax __FILE__ Description The __FILE__ constant reflects the name of the current file being parsed by the PHP interpreter. __LINE__ Syntax __LINE__ Description The __LINE__ constant reflects the line number of the current file being parsed by the PHP interpreter. E_ERROR Syntax E_ERROR Description PHP Developer’s Dictionary IT-SC book 67 The E_ERROR constant contains a nonparsing and nonrecoverable error that has occurred. Additionally, you can use the error_reporting() function to specify the level of error reports you want out of this function. E_NOTICE Syntax E_NOTICE Description The E_NOTICE constant contains what may or may not be an error in your PHP code, but either way, it does not prevent the code from completing execution. Additionally, you can use the error_reporting() function to specify the level of error reports you want out of this function. E_PARSE Syntax E_PARSE Description The E_PARSE constant reflects the fact that the PHP parser failed because of a syntax problem and cannot recover. Additionally, you can use the error_reporting() function to specify the level of error reports you want out of this function. E_WARNING Syntax E_WARNING Description The E_WARNING constant contains an error in your PHP code, but does not prevent the code from completing execution. Additionally, you can use the error_reporting() function to specify the level of error reports you want out of this function. PHP Developer’s Dictionary IT-SC book 68 PHP_OS Syntax PHP_OS Description The PHP_OS constant reflects the name of the operating system that is currently parsing and interpreting the PHP code. If you are running scripts across multiple platforms, this enables you to check the operating system before performing any system-specific tasks. PHP_VERSION Syntax PHP_VERSION Description The PHP_VERSION constant contains a string that reflects the exact version of the PHP interpreter. FALSE Syntax FALSE Description The FALSE constant reflects a Boolean false value. TRUE Syntax TRUE PHP Developer’s Dictionary IT-SC book 69 Description The TRUE constant reflects a Boolean true value. Control Structures and Statements Control structures and statements are items that all programmers use to control the flow of their programs. This includes most looping commands, such as if or while statements, and other commands, such as break and continue , that can be used to control the program execution in the body of a control structure. break Syntax break [int num] Description The break statement enables you to break out of an if , switch , or while control structure. The optional num value can be used to tell the parser how many control structures to break out of. For instance, if you used a break statement inside an if statement that was inside a while statement itself, you could use break 2 to break out of both statements. Using break 1, which is the default implied value when not passed, would simply break you out of the if statement. if($num == 5){ // do something here if($string == "go"){ // do more here break 2; // breaks outside of both if statements } } // the break 2 will start back here if executed continue Syntax continue [int num] Description . of error reports you want out of this function. PHP Developer’s Dictionary IT-SC book 68 PHP_ OS Syntax PHP_ OS Description The PHP_ OS constant reflects the name of the operating. method works // in the PHP programming language. /* */ Syntax /* comment */ Description The /* */ PHP element is another method of defining a comment in the PHP language. This. the PHP code. If you are running scripts across multiple platforms, this enables you to check the operating system before performing any system-specific tasks. PHP_ VERSION Syntax PHP_ VERSION