Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition

Chapter 3 Answers

1. The tag used to start PHP interpreting code is <?php ... ?>, which can be shortened to <? ... ?>.

2. You can use // for a single-line comment or /* ... */ to span multiple lines.

3. All PHP statements must end with a semicolon (;).

4. With the exception of constants, all PHP variables must begin with $.

5. A variable holds a value that can be a string, a number, or other data.

6. $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.

7. 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.

8. Variable names are case-sensitive. $This_Variable is not the same as $this_variable.

9. You cannot use spaces in variable names, as this would confuse the PHP parser. Instead, try using the _ (underscore).

10. To convert one variable type to another, reference it and PHP will automatically convert it for you.

11. 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 ...