PHP Conditions and Input

Introduction

If you want to make your Web pages do significant and interesting things with PHP, you will eventually need to let the PHP code make some decisions about the information, events, and/or data that it is dealing with. This handout will teach you how to deal with different values and conditions in the page.

Before we talk about conditions, though, we will first look at a handy way to get some information from your Web page's user. I am referring to forms.

Forms

We will see forms again later in the semester. For now, this section describes a simple way to get information from the user of your page, and to display submitted form data in another page, usually called the action page. (The term "action page" refers to the page which receives submitted form data, because the <form> tag has an action attribute which tells the browser where to send the submitted data.)

First, here is a simple HTML form: This is page testFormData2.html.

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="myStyles.css">
  <title>Display Form Data</title>
</head>

<body>
  <div id="mainDiv">
    <form name="theForm" action="displayFormInfo2.php"
          method="post">
      Please enter your name:
      <input type="text" name="theName" id="theName" />
      <br />
      <br />
      Please enter your phone number:
      <input type="text" name="theNumber" id="theNumber" />
      <br />
      <br />
      <input type="submit" value="Send the form information" />
    </form>
  </div>
</body>
</html>

Secondly, here is the PHP action page that displays the form information: This is page displayFormInfo2.php.

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="myStyles.css">
  <title>Display Form Info</title>
</head>

<body>
  <div id="mainDiv">
    <h3>This is the form data that was sent:</h3>
    <?php
      print "The Name: ";
      print $_POST["theName"];
      print "<br />";
      print "The Number: ";
      print $_POST["theNumber"];
    ?>
  </div>
</body>
</html>

You can see the sample pages running here.

Please note these points about the above code:

The method attribute in the <form> tag has a value of "post".
The action attribute in the <form> tag has a value that points to another page on the Web server; in this case, it is the second page, displayFormInfo2.php. It is this second, action page, which receives the information from the form page when the submit button is clicked.
The PHP server automatically places the form data (when the method is "post") into a variable called $_POST, when the form's data are submitted to the action page. This $_POST variable is an array, which we will talk about in more detail later in the semester.
For now, note that arrays are like indexed lists of items. The index value for the $_POST array is a string (text) in quotes and contained within square brackets, like this:
```
$_POST["theName"]
```
The strings which become the index values for the $_POST array come from the name attributes in the form's input fields. It is the name attributes in the form, in fact, which connect the form itself to the values that PHP puts into the $_POST array.

Another Form Display

In this section, we will use an HTML form page that is almost identical to the HTML form page in previous section, but we will see another way to display form information in a PHP page.

First, here is the HTML form page: This is page testFormData3.html.

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="myStyles.css">
  <title>Display Form Data</title>
</head>

<body>
  <div id="mainDiv">
    <form name="theForm" action="displayFormInfo3.php"
          method="post">
      Please enter your name:
      <input type="text" name="theName" id="theName" />
      <br />
      <br />
      Please enter your phone number:
      <input type="text" name="theNumber" id="theNumber" />
      <br />
      <br />
      <input type="submit" value="Send the form information" />
    </form>
  </div>
</body>
</html>

The PHP action page is displayFormInfo3.php:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="myStyles.css">
  <title>Display Form Info</title>
</head>

<body>
  <div id="mainDiv">
    <h3>A Form Letter:</h3>
    <?php
      $theNumber = $_POST["theNumber"];
      
      print <<<HERE
      Thank you, {$_POST["theName"]}, for your request.
      <br />
      <br />
      We will contact you at phone number $theNumber
      within 3 business days.
      <br />
      <br />
      Sincerely,
      <br />
      <br />
      The Management
HERE;
    ?>
  </div>
</body>
</html>

You can see the sample pages running here.

Please note these points about the above code:

In the action page, we create a non-array variable at the top of the PHP section. (The technical term for a simple, non-array variable is "scalar variable".) In this page, the scalar variable is $theNumber.
This variable gets one of the form-field values that were sent to the server from the HTML form. We use an assignment statement to put the form's (array) value into our simple (scalar) variable.
This scalar variable is used later in the page, in the multi-line string.
If you want to use $_POST variables (or other array variables) directly in the multi-line string without using a separate (scalar) variable, you need to use a special variable syntax called complex (curly) syntax. (This complex (curly) syntax is also useful for array variables in regular, double-quoted strings, too.)

In the sample code above, for example, the array variable
```
$_POST["theName"]
```
is inserted directly into the string with code like this:
```
  Thank you, {$_POST["theName"]}, for your request.
```
Note the curly braces around the built-in $_POST variable.

If you try to put the form variable's value into the string without the curly braces, you will get a syntax error message from the PHP parser/server.
Also, please note that this use of the curly braces is completely different from the standard block-creating use of curly braces that we talked about in the section "Curly Braces (Code Blocks)", in a previous class.

Using the if Statement to Control Page Flow

The simplest way for you to instruct a PHP page to make a decision, is to use the if statement.

For the next several handout sections, we will use the same input form as we used at the beginning of this handout. But for the action pages we will use several different pages which illustrate the conditions that we are discussing.

The Condition Form 1 Page demonstrates the use of an if statement.

The code for the action page is shown below. This is page conditionAction1.php:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="myStyles.css">
  <title>Simple IF Statement</title>
</head>

<body>
  <div id="mainDiv">
    <h3>A Form Letter:</h3>
    <?php
      $theName = $_POST["theName"];
      $theNumber = $_POST["theNumber"];
      
      if ($theName == 'Jim')
      {
        echo "<p>Welcome back, Mr. Link!</p>\n";
      }
      
      echo "<p>Your number is " . $theNumber . ".</p>\n";
    ?>
  </div>
</body>
</html>

Please note these points about the above action page:

The line that echoes "Welcome back, Mr. Link!" into the page doesn't happen every time the page is loaded. It only happens if a certain condition is TRUE.
In English, the conditional test is "If $theName is equal to 'Jim'".
In PHP, the conditional test is if ($theName == 'Jim').
In the PHP version of the conditional test, there is a set of parentheses around the condition after the keyword if. (A keyword is a word or command which is reserved by PHP for its own use. You may not use keywords as variable names, for instance.)
The code that is run if the condition is TRUE, is between the opening and closing curly braces ({ and }). You can put as many lines (statements) of code as needed, in between the opening and closing braces.
The previous item in this list brings us to the first of
Jim's Rules of Survival

Jim's Rule of Survival #1:
Always use curly braces in if statements.
Any expression that can return TRUE or FALSE can be used as a condition.
Expressions or values that are either TRUE or FALSE are called "Boolean" values. The keywords TRUE and FALSE are NOT case-sensitive, so they can be typed as TRUE, FALSE, true, false, True, or False in PHP.
Equality in PHP is tested with two equal signs.

That last point is extremely important. The following two PHP statements are both correct syntactically, but they do very different things:

$x = 5;

assigns the value 5 to the variable $x, using the assignment operator, which is =; and

$x == 5

tests to see if the value 5 is in the variable $x, using the comparison operator for equality, which is ==.

Comparison Operators

There are other types of comparison that you can do in PHP. The following table shows the comparison operators that you can use in conditional statements:

Operator	Description
==	Equal to
<	Less than
>	Greater than
<=	Less than or equal to
>=	Greater than or equal to
!=	Not equal to

The else Clause

You can also code your page so that it does something if the condition that you are testing for is FALSE.

In PHP, one way that you tell the page to do something if the condition is FALSE, is to use the else clause.

The Condition Form 2 Page demonstrates the use of an else clause.

The code for the action page is shown below. This is page conditionAction2.php:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="myStyles.css">
  <title>Simple IF and ELSE Statement</title>
</head>

<body>
  <div id="mainDiv">
    <h3>A Form Letter:</h3>
    <?php
      $theName = $_POST["theName"];
      $theNumber = $_POST["theNumber"];
      
      if ($theName == 'Jim')
      {
        echo "<p>Welcome back, Mr. Link!</p>\n";
      }
      else
      {
        echo "<p>Welcome, honored guest!</p>\n";
      }
      
      echo "<p>Your number is " . $theNumber . ".</p>\n";
    ?>
  </div>
</body>
</html>

Please note these points about the above action page:

If the condition is FALSE, the code following the else keyword is run.
The code that is run if the condition is FALSE, is between the opening and closing curly braces ({ and }) that follow the else keyword. You can put as many lines (statements) of code as needed, in between the opening and closing braces.
This type of code guarantees that something will be put into the page, depending on the results of the condition (comparison).

Logical Operators

Sometimes you need to combine conditions in the conditional expression of an if statement.

The following table shows the logical operators that you can use in combining conditional statements:

Logical Operator	Description
&&	And - returns true if both the left operand and right operand return a value of true; otherwise, it returns false
\|\|	Or - returns true if either the left operand or right operand returns a value of true. If both the left and right operands return a value of false, this operator returns false.
!	Not - returns true if an expression is false, and returns false if an expression is true

The && and || operators are binary operators, which means that there are two things (technically called "operands") to do something with.

The ! operator is a unary operator, which means that there is only one thing (technically called the "operand") to do something with.

The following two tables should help you understand under what conditions the logical operators return true or false:

If Condition 1 is	and Condition 2 is	the result of Condition 1 AND Condition 2 is
true	true	true
true	false	false
false	true	false
false	false	false

If Condition 1 is	and Condition 2 is	the result of Condition 1 OR Condition 2 is
true	true	true
true	false	true
false	true	true
false	false	false

Here is an example of how you can combine conditions. This is file logicalOperators.php:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="myStyles.css">
  <title>Logical Operators</title>
</head>

<body>
  <div id="mainDiv">
    <h3>Logical Operators</h3>
    <?php
      $a = 5;
      $b = 7;
      $c = FALSE;
      
      if ($a > 1 && $b < 10) // If $a is greater than 1 AND $b is less than 10...
      {
        echo "The AND condition succeeded.<br>\n";
      }
      
      if ($a > 10 || $b < 10)  // If $a is greater than 10 OR $b is less than 10...
      {
        echo "The OR condition succeeded.<br>\n";
      }
      
      if (!$c)  // If NOT $c...   which is the same as If $c is NOT TRUE...
      {
        echo "The NOT condition succeeded.<br>\n";
      }
    ?>
  </div>
</body>
</html>

Single-Page Form Submission

There are many ways to prevent errors such as "undefined index" when you include an HTML form and its action code in the same page. The code sample given in this section is just one way to prevent such errors.

Here is a sample page which has an HTML form and the PHP action code in the same page. This is page singlePageForm.php, which you can see running here.

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="myStyles.css">
  <title>Single-Page Form</title>
</head>

<body>
  <div id="mainDiv">
    <div id="formDiv">
      <?php
      if (!isset($_POST["formSubmitted"]))
      {
    ?>
      <form name="theForm" action="singlePageForm.php" method="post">
        <input type="hidden" name="formSubmitted" value="1">
        <h3>Type in a color:</h3>
        <input type="text" name="color">
        <h3>Type in an animal name:</h3>
        <input type="text" name="animal">
        <h3>Type in country name:</h3>
        <input type="text" name="country">
        <br>
        <br>
        <input type="submit" value="Tell a Story">
      </form>
      <?php
      }
      else
      {
        echo "<p>\n";
        echo "The {$_POST['color']} {$_POST['animal']} took a nap in {$_POST['country']}.";
        echo "<p>Please <a href='singlePageForm.php'>go back</a> and tell another story.</p>\n";
      }
    ?>
    </div>
  </div>
</body>
</html>

Please note these points about the above code:

The form's action attribute gives the current/same page that the form is in.
There is a hidden input field in the form, which is used solely for the purpose of checking to see if the form has been submitted. This hidden input field's name attribute in this form has the value "formSubmitted", which can be any unique name.
The if statement in this page checks on the $_POST["formSubmitted"] variable/array item's NOT being in memory. As a reminder, the explanation point in PHP is used as a logical NOT operator.
If the $_POST["formSubmitted"] variable/array item is NOT in memory, it means that the form has NOT been submitted. Actually, you could test for almost any form input field's being in memory; in this form we are using a hidden input field purely as a convenience.

Handling Multiple Conditions

You can use multiple else clauses in a series of else if statements. (And see the next section for an even better way to handle multiple values.)

The Condition Form 3 Page demonstrates the use of multiple else if clauses.

The code for the action page is shown below. This is page conditionAction3.php:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="myStyles.css">
  <title>Multiple IF ELSE Statements</title>
</head>

<body>
  <div id="mainDiv">
    <h3>A Form Letter:</h3>
    <?php
      $theName = $_POST["theName"];
      $theNumber = $_POST["theNumber"];
      
      if ($theName == 'Jim')
      {
        echo "<p>Welcome back, Mr. Link!</p>\n";
      }
      else if ($theName == 'Sam')
      {
        echo "<p>Welcome back, Mr. Johnson!</p>\n";
      }
      else if ($theName == 'Sarah')
      {
        echo "<p>Welcome back, Ms. Smith!</p>\n";
      }
      else
      {
        echo "<p>Welcome, honored guest!</p>\n";
      }
      
      echo "<p>Your number is " . $theNumber . ".</p>\n";
    ?>
  </div>
</body>
</html>

Please note these points about the above action page:

There is one large logical code structure, which has multiple if and else clauses.
If none of the conditions is TRUE, the code in the final else clause is run.

The switch Statement

PHP has a decision structure that you can use instead of multiple else if statements. This structure is the switch statement and it is used when you are comparing a variable to many possible values.

The Condition Form 4 Page looks a lot like the previous page, but it uses a switch statement.

The code for the action page is shown below. This is page conditionAction4.php:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" href="myStyles.css">
  <title>The Switch Statement</title>
</head>

<body>
  <div id="mainDiv">
    <h3>A Form Letter:</h3>
    <?php
      $theName = $_POST["theName"];
      $theNumber = $_POST["theNumber"];
      
      switch ($theName)
      {
        case 'Jim':
        echo "<p>Welcome back, Mr. Link!</p>\n";
        break;
        
        case 'Sam':
        echo "<p>Welcome back, Mr. Johnson!</p>\n";
        break;
        
        case 'Sarah':
        echo "<p>Welcome back, Ms. Smith!</p>\n";
        break;
        
        default:
        echo "<p>Welcome, honored guest!</p>\n";
      }  // end switch
      
      echo "<p>Your number is " . $theNumber . ".</p>\n";
    ?>
  </div>
</body>
</html>

Please note these points about the above action page:

The switch structure begins by defining an expression. In this code, the expression is ($theName). The value in the expression is the value that will be tested/compared to look for a matching value in the following case statements.
Then the switch structure defines a series of possible matches for the expression. Each possible match is in a case statement.
There is a colon following each case statement.
Each case ends with a break statement. This break statement tells PHP that the proper case has been run, and now it's time to get out of the switch structure.
The last case is a default case. This default case is a lot like the final else statement in the else if clauses in some of the previous code that we looked at.

Richland College Multimedia Learning Center

PHP Conditions and Input

Introduction

Forms

Another Form Display

Using the if Statement to Control Page Flow

Jim's Rules of Survival

Jim's Rule of Survival #1:Always use curly braces in if statements.

Comparison Operators

The else Clause

Logical Operators

Single-Page Form Submission

Handling Multiple Conditions

The switch Statement

Jim's Rule of Survival #1:
Always use curly braces in if statements.