Show description

As you’ve already seen, a Boolean value is either true or false. PHP automatically evaluates expressions as either true or false when needed, although as you’ve already seen, you can use settype() or casting to explicitly convert a value to a Boolean value if necessary. 0) ❑ An empty string (“ “) ❑ The string zero (“0”) ❑ An array with zero elements ❑ The special type null (including any unset variables) ❑ A SimpleXML object that is created from an empty XML tag (more on SimpleXML in Chapter 19) All other values are considered true in a Boolean context.

For example: echo “Shaken, “ . “not stirred”; // Displays “Shaken, not stirred” You can also concatenate more than two strings at once. ” echo “Books catch fire at “ . ( (5/9) * ($tempF-32) ) . = — which was mentioned earlier in the chapter. It’s useful when you want to join a new string onto the end of an existing string variable. For example, the following two lines of code both do the same thing — they change the string variable $x by adding the string variable $y to the end of it: $x = $x .

Then, when you run the preceding line of code, the script outputs the sum of those two values. Re-run the script with different values for $x and $y, and you get a different result. Naming Variables A variable consists of two parts: the variable’s name and the variable’s value. Because you’ll be using variables in your code frequently, it’s best to give your variables names you can understand and remember. Like other programming languages, PHP has certain rules you must follow when naming your variables: ❑ Variable names begin with a dollar sign ($) ❑ The first character after the dollar sign must be a letter or an underscore ❑ The remaining characters in the name may be letters, numbers, or underscores without a fixed limit Variable names are case-sensitive ($Variable and $variable are two distinct variables), so it’s worth sticking to one variable naming method — for example, always using lowercase — to avoid mistakes.