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Are never reset and are only within the scope of the function. You cannot assign the result of an expression in their definitions.
They are provided by the PHP environment but are global within the program, accessible absolutely everywhere. All of the superglobals (except for $GLOBALS) are named with a single initial underscore and only capital letters;
Using the htmlentities is important because...
Using the htmlentities function for sanitization is an important practice in any circumstance where user or other third-party data is being processed for output, not just with superglobals.
What tag is used to cause PHP to start interpreting program code? And what is the short form of the tag?
The tag used to start PHP interpreting code is <?php ... ?>, which can be shortened to <? ... ?> but is not recommended practice.
What are the two types of comment tags?
You can use // for a single-line comment or / ... / to span multiple lines.
Which character must be placed at the end of every PHP statement?
All PHP statements must end with a semicolon (;).
Which symbol is used to preface all PHP variables?
With the exception of constants, all PHP variables must begin with $.
What is the difference between $variable = 1 and $variable == 1?
$variable = 1 is an assignment statement, whereas $variable == 1 is a comparison operator. Use $variable = 1 to set the value of $variable. Use $variable == 1 to find out later in the program whether $variable equals 1. If you mistakenly use $variable = 1 where you meant to do a comparison, it will do two things you probably don't want: set $variable to 1 and return a true value all the time, no matter what its previous value was.
Why do you suppose an underscore is allowed in variable names (e.g., $current_user) whereas hyphens are not (e.g., $current-user)?
A hyphen is reserved for the subtraction operators. A construct like $current-user would be harder to interpret if hyphens were also allowed in variable names and, in any case, would lead programs to be ambiguous.
Are variable names case-sensitive?
Variable names are case-sensitive. So, for example,$This_Variable is not the same as $this_variable.
Can you use spaces in variable names?
You cannot use spaces in variable names, as this would confuse the PHP parser. Instead, try using the _ (underscore).
How do you convert one variable type to another (say, a string to a number)?
To convert one variable type to another, reference it and PHP will automatically convert it for you.
What is the difference between ++$j and $j++?
There is no difference between ++$j and $j++ unless the value of $j is being tested, assigned to another variable, or passed as a parameter to a function. In such cases, ++$j increments $j before the test or other operation is performed, whereas $j++ performs the operation and then increments $j.
Are the operators && and and interchangeable?
Generally, the operators && and and are interchangeable except where precedence is important, in which case && has a high precedence, while and has a low one.
How can you create a multiline echo or assignment?
You can use multiple lines within quotations marks or the <<<_END ... _END; construct to create a multiline echo or assignment. The closing tag must begin at the start of a line, and end with a semicolon followed by a new line.
Can you redefine a constant?
You cannot redefine constants because, by definition, once defined they retain their value until the program terminates.
What is the difference between the echo and print commands?
The echo and print commands are similar in that they are both constructs, except that print behaves like a PHP function and takes a single argument, while echo can take multiple arguments.
What is the purpose of functions?
The purpose of functions is to separate discrete sections of code into their own, self-contained sections that can be referenced by a single function name.
How can you make a variable accessible to all parts of a PHP program?
You can make a variable accessible to all parts of a PHP program by declaring it as global.
If you generate data within a function, what are a couple of ways to convey the data to the rest of the program?
If you generate data within a function, you can convey the data to the rest of the program by returning a value or modifying a global variable.