Sams Teach Yourself PHP, MySQL and Apache All in One (2012)

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The important thing to note here is that the shift to HTML mode on line 4 occurs only if the condition of the if statement is fulfilled. This can save you the bother of escaping quotation marks and wrapping our output in echo() statements. This approach might, however, affect the readability of the code in the long run, especially if the script grows larger.

Summary

In this chapter, you learned about control structures and the ways in which they can help to make your scripts flexible and dynamic. Most of these structures reappear regularly throughout the rest of the book.

You learned how to define an if statement and how to provide for alternative actions with the elseif and else clauses. You learned how to use the switch statement to change flow according to multiple equivalence tests on the result of an expression. You learned about loops—in particular, the while and for statements—and you learned how to use break and continue to prematurely end the execution of a loop or to skip an iteration. You learned how to nest one loop within another and saw a typical use for this structure. You also looked at a technique for using PHP start and end tags in conjunction with conditional code blocks, to alleviate having to escape (use the backslash in front of) special characters such as the quotation mark and dollar sign.

You should now know enough of the basics to write scripts of your own that make decisions and perform repetitive tasks. In the next chapter, you learn how to add even more power to your applications. You learn how functions enable you to organize your code, preventing duplication and improving reusability.

Q&A

Q. Must a control structure’s test expression result in a Boolean value?

A. Ultimately, yes. But in the context of a test expression, 0, an undefined variable, or an empty string is converted to false. All other values evaluate to true.

Q. Must I always surround a code block in a control statement with brackets?

A. If the code you want executed as part of a control structure consists of only a single line, you can omit the brackets. However, the habit of always using opening and closing brackets, regardless of structure length, is a good one.

Workshop

The workshop is designed to help you review what you’ve learned and begin putting your knowledge into practice.

Quiz

1. How do you use an if statement to print the string "Youth message" to the browser if an integer variable, $age, is between 18 and 35? If $age contains any other value, the string "Generic message" should be printed to the browser.

2. How do you extend your code in question 1 to print the string "Child message" if the $age variable is between 1 and 17?

3. How do you create a while statement that increments through and prints every odd number between 1 and 49?

4. How do you convert the while statement you created in question 3 into a for statement?

Answers

1.

$age = 22;

if (($age >= 18) && ($age <= 35)) {
echo "Youth message";
} else {
echo "Generic message";
}

2.

$age = 12;

if (($age >= 18) && ($age <= 35)) {
echo "Youth message";
} elseif (($age >= 1) && ($age <= 17)) {
echo "Child message";
} else {
echo "Generic message";
}

3.

$num = 1;

while ($num <= 49) {
echo $num."<br />";
$num += 2;
}

4.

for ($num = 1; $num <= 49; $num += 2) {
echo $num."<br />";
}

Activities

1. Review the syntax for control structures. Think about how the techniques you’ve learned will help you in your scripting. Perhaps some of the script ideas you develop will be able to behave in different ways according to user input or will loop to display an HTML table.

2. Start to build the control structures you will be using. Use temporary variables to mimic user input or database queries for the time being.