PHP and MySQL by Example- P6

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A parse error occurred because single quotes were embedded within double quotes. This can be fixed by concatenating the strings as follows: echo $book['Title'] . ""; or by surrounding the array element with curly braces: echo "{$book['Title']}" Do not eliminate the quotes around the key as shown here: echo $book[Title]; as PHP will treat the key Title as a constant, not as a string. You might inadvertently use a key value that has been defined somewhere else as a constant to produce the error message “E_NOTICE (undefined constant).” Mixing Elements in an Array The index/key value in an array can be a positive or negative number or a string, and the value associated with it can be a string, a number, another array, and so on. If an index value is not given, PHP provides a numeric index, incrementing the index of the next position in the array by 1. Example 8.7 demonstrates how the index and the value of the elements can be mixed. The output is shown in Figure 8.11. Example 8.7. Using a Negative Index
4 Although the value 'orange' was not explicitly assigned an index, PHP will add 1 to the previous numeric index value. Because that index was –1, the index for 'orange' will be assigned 0. 5 Here the index is a string, "brown", associated with a value, "burnt sienna". Using a string will have no effect on the numeric indexes. 6 This line is commented out, but provided to demonstrate the use of curly braces when using arrays and nested quotes; that is, quotes within quotes. When an array element is enclosed within a string in double quotes, the curly braces allow the key to be surrounded by single quotes, without causing a PHP error. Without the curly braces the error is: Parse error: syntax error, unexpected T_ENCAPSED_AND_WHITESPACE, expecting T_STRNG or TVARIABLE orT_NUM_STRING inC:\\wamp\php-‐ on line 18 Figure 8.11. Mixed array elements. Output from Example 8.7. 8.1.3. Printing an Array There are a number of ways to print the contents of an array. PHP provides built-in functions to display all of the keys and values, or you can use loops. We discuss the built-in functions first. The print_r() Function The print_r() built-in function displays detailed information about a variable, such as its type, length, and contents. It displays the value of a string, integer, or float. In the case of arrays, print_r() displays all of the elements of an array; that is, the key–value pairs. (Use the HTML tag, to display each element on a separate line; otherwise, the output is displayed on one line.) If you would like to capture the output of print_r() in a variable, set the return parameter to boolean TRUE. The print_r() function can also be useful when debugging a program. Remember that print_r() will move the internal array pointer to the end of the array. Use reset() to bring it back to the beginning. PHP 5 appears to reset the pointer automatically after using print_r(). Example 8.8 demonstrates the print_r() function. The output is shown in Figure 8.12. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Format bool print_r ( mixed expression [, bool return] ) Example: print_r($colors); // Display the contents of the array $list=print_r( $colors, true); // Save the return value in $list reset($colors); // Move internal array pointer to array beginning Example 8.8. The print_r() Function Explanation 1 A numeric array called $colors is created with four elements. 2 An associative array called $book is created with key–value pairs. 3 The print_r() function displays the array in a humanly readable format, numeric indexes on the left of the => operator and the value of the elements on the right side. Use the HTML tag to present the array on separate lines; otherwise it will be displayed as one long line. 4 The print_r() function displays the associative array, key–value pairs in an easy-‐to-‐read format. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Figure 8.12. Printing an array with the print_r() function. Output from Example 8.8. Example 8.9. The print_r() Function Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Explanation 1 By giving print_r() an additional boolean argument of TRUE, you can capture the output of print_r() in a variable. 2 The $display variable contains the output of the print_r() function; that is, the contents of the array. See Figure 8.13. 3 The reset() function puts the internal array pointer back at the beginning of the array. The PHP manual suggests using this function to reset the array pointer, but in PHP 5 it is not necessary. Figure 8.13. Saving the output from print_r() in a variable. Output from Example 8.9. The var_dump() Function The var_dump() function displays the array (or object), the number of elements, and the lengths of each of the string values. It also provides output with indentation to show the structure of the array or object. (See Chapter 17, “Objects,” for more on objects.) Example 8.10 demonstrates the var_dump() function. The output is shown in Figure 8.14. Format void var_dump ( mixed expression [, mixed expression [, ...]] ) Example: $states=array('CA' => 'California','MT'=>'Montana','NY'=>'New York'); var_dump($states); // Dumps output in a structured format Example 8.10. The var_dump() Function Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Explanation 1 The numeric array, $colors, is assigned a list of colors. 2 The associative array, $book, is assigned key–value pairs. 3 The var_dump() function takes the name of the array as its argument, and displays the output by first printing the number of elements in the array, index value, and then the number of characters in each of the assigned string values and its value. See Figure 8.14. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Figure 8.14. Printing an array with the var_dump() function. Output Example 8.10. 8.1.4. Using Loops to Access Array Elements Loops make it easy to step through an array. The for and while loops are useful for numeric arrays where you can determine the size, and starting point of the array is usually 0, incremented by 1 for each element. The best way to loop through an associative array is with the foreach loop, although you can use this loop for numerically indexed arrays as well. The for Loop The for loop can be used to iterate through a numeric array. The initial value of the for loop will be the first index value of the array, which will be incremented each time through the loop until the end of the array is reached. Example 8.11 demonstrates how the for loop is used to view each element of an array. The output is displayed in Figure 8.15. Example 8.11. The for Loop Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Elements Explanation 1 The numeric array, $colors, is assigned a list of colors. 2 The first argument to the for loop, $i = 0, sets the initial value of $i to 0, which represents the first index in the array. If the index value, $i, is less than the size of the array (returned from the count() function), the loop body is entered, after displaying the color, the third argument of the for loop is executed; that is, increment the value of $i by 1. 3 Each time through the loop, the next element in the $colors array is displayed in a table cell. Figure 8.15. Using the for loop to loop through an array. Output from Example 8.11. The while Loop The while loop can be used to iterate through a numeric array as shown in Examples 8.12 and 8.13. By setting the initial value to 0, the loop will iterate from the first element of the array (assuming that the array starts at element zero) until it reaches the end of the array. The count() or sizeof() functions can be used to find the length of the array. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Example 8.12. The while Loop Elements Explanation 1 A numeric array called $colors is created and assigned string values. 2 Variable, $i, set to 0, will be the initial value in the loop, and will used as the array’s index. 3 The count() function returns the number of elements in the array. The while expression tests that the value of $i is less than the size of the array. 4 The value of $i will be used as the index value of the array, $colors. Each time through the loop, the value will be incremented by 1. In this example, the value of the element, a color, will be used as the background color for the current row, and as the text printed within the table’s data cell. See Figure 8.16. 5 The value of $i is incremented by 1. If you forget to increment $i, the loop will go forever because $i will always be less than the size of the array. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Figure 8.16. Using the while loop to iterate through an array. Output from Example 8.12. Example 8.13. Code View: Table Colors Colored Rows
6 $i++; // Increment the value of the loop counter 7 } ?> Explanation 1 An array called $colors is assigned four color values. 2 The variable, $i, is initialized to 0. 3 The while loop evaluates the expression in parentheses. Is the value of $i less than 8? If it is, the loop body is entered. 4 The index value of the $colors array is divided by 4 and the remainder (modulus) is replaced as the new index value. 5 The first time in the loop the index is 0. The value $color[0] is "orange" and will be filled in the table for a row of 5 table cells. See Figure 8.17. 6 The value of $i is incremented by 1. Next time through the loop, $color[1] is "lightgreen" and that color will fill a row of table cells. 7 This is the closing brace for the while loop. Figure 8.17. The while loop and arrays. Output from Example 8.13. The foreach Loop The foreach statement is designed to work with both numeric and associative arrays (works only on arrays). The loop expression consists of the array name, followed by the as keyword, and a user-defined variable that will hold each successive value of the array as the loop iterates. The expression in the foreach statement can include both the key and value as shown in Example 8.14. The foreach loop operates on a copy of the original array. If you change the value of an element of the array, it will only change the copy, not the value in the original. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Format (Numeric Array) foreach ($array_name as $value){ do-something with the element's value; } foreach($array_name as $index=>$value){ do-something with the element's index and value } Example: $suit=("diamond", "spade", "club", "heart"); foreach ( $suit as $card_type){ echo $card_type . ""; // displays: diamond } spade club heart (Associative Array) foreach ($array_name as $key => $variable){ do-something $key and/or $variable; } Example: $courses=("101A"=>"Intro to CS", "200B"=>"Data Structures", "130A"=>"Visual Basic" ); foreach ( $courses as $number=>$class_name){ echo $number . '=>' . $class_name . ""; // displays keys // and values } Example 8.14. Code View: The foreach Loop
); 3 foreach ($colors as $value){// Each value is stored in $value echo "$value "; } echo ""; 4 foreach ($employee as $key => $value){// Associative array echo "employee[$key] => $value"; } ?> Explanation 1 A numeric array of four colors is defined. 2 An associative array of four key–value pairs is defined. 3 The foreach loop is used to iterate through each element of the $colors array. The expression $colors as $value, means: In the $colors array assign the value of each element to the variable $value, one at a time, until the array ends. Each value will be displayed in turn. See Figure 8.18. 4 This foreach loop iterates through each key–value pair of an associative array, called employee. The array name is followed by the as keyword and a variable to represent the key, called $key, followed by the => operator, and a variable to represent the value, called $value. Figure 8.18. Looping through an array with the foreach loop. Output from Example 8.14. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Modifying a Value by Reference with a foreach Loop As of PHP 5, you can easily modify an array’s elements by preceding the value after the as keyword with &. This will assign by reference instead of copying the value; that is, whatever you do to the array while in the loop will change the original array, not a copy of it. Example 8.15. Code View: The foreach Loop--Changing Values by Reference Original array Array has been changed Explanation 1 A variable, $val, is assigned the string,"hello". 2 A numeric array, called $years, is assigned four numbers. 3 The print_r() function prints the original array. See Figure 8.19. 4 In the foreach expression the variable $val is used as a reference to each element of the $years array. The & preceding the variable name makes it a reference. Any changes made to the value that $val references will change the original array. 5 1900 is added to each value in the array via the reference, $val. 6 Because $val is a global variable (i.e., visible throughout the program), its original value is changed in the foreach loop, and the last value assigned to it remains after the loop exits. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
is changed in the foreach loop, and the last value assigned to it remains after the loop exits. 7 The print_r() function prints the modified array. See Figure 8.19. Figure 8.19. Modifying values by reference. Output from Example 8.15. 8.1.5. Checking If an Array Exists PHP makes it possible to check to see if an array exists, and to check for the existence of keys, values, or both. See Table 8.2. Table 8.2. Functions to Check for Existence of an Array Function What It Does array_key_exists() Checks if the given key or index exists in the array in_array() Checks if a value exists in an array is_array() Checks if the variable is an array; returns TRUE or FALSE Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Example 8.16 demonstrates how to perform array checks using the functions in Table 8.2. The output is displayed in Figure 8.20. Example 8.16. Code View: Checking for Existence of an Array or Element Does it Exist? Explanation 1 A simple scalar variable called $country is assigned the string "USA". 2 An associative array called $states is assigned key–value pairs. 3 The is_array() built-‐in function returns true if its argument is an array, and false if it is not. $states is not an array. 4 The array_key_exists() built-‐in function returns true if its argument is the key or index in an array. 5 The in_array() built-‐in function returns true if its argument is a value that exists in an array. The array value "Montana" does exist in the $states associative array. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Figure 8.20. Checking an array’s existence. 8.1.6. Creating Strings from Arrays and Arrays from Strings In Chapter 6, “Strings,” we discussed strings and their many functions. Now that we have learned about arrays, PHP provides functions that serve the dual purpose of creating arrays from strings and strings from arrays (see Table 8.3). Table 8.3. Arrays and Strings Function What It Does explode() Splits up a string by a specified delimiter and creates an array of strings implode() Creates a string by gluing together array elements by a specific separator join() Alias for implode() split() Splits up a string into an array by a regular expression (see Chapter 12, “Regular Expressions and Pattern Matching”) The implode() Function The implode() function creates a string by joining together the elements of an array with a string delimiter, called the glue string. As of PHP 4.3.0, the glue parameter of implode() is optional and defaults to the empty string(""). Another name for implode() is its alias, join(). The implode() function returns a string containing a string representation of all the array elements in the same order, with the glue string between each element. Format string implode ( string glue, array elements ) Example: $stats_array = array('name', 'ssn', 'phone'); // implode() creates a string from an array $stats_string = implode(",", $array); The explode() Function The explode() function splits up a string and creates an array, the opposite of implode(). The new array is created by splitting up the original string into substrings based on the delimiter given. The delimiter is what you determine is the word separator, such as a space or comma. If given a limit, the new array will be limited to that many substrings, and the last one will contain the rest of the string. See also “The preg_split() Function—Splitting Up Strings” on page 510. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Example 8.17 demonstrates how the explode function works. Its output is displayed in Figure 8.21. Format array explode(string separator, string string [, int limit]) Example: $fruit = explode(" ", "apples pears peaches plums") //Creates a 4-element array $fruit = explode("|", "apples|pears|peaches|plums",3) echo $fruit[0], $fruit[1], $fruit[2]; // Creates a 3-element array Example 8.17. explode() Array
Figure 8.21. Converting a string to an array with the explode() function. Output from Example 8.17. 8.1.7. Finding the Size of an Array PHP provides built-in functions to count the number of elements in an array. They are count(), sizeof(), and array_count_values(). Example 8.18 demonstrates how to find the size of a multidimensional array. Table 8.4. Functions to Find the Size of an Array Function What It Does array_count_values() Returns an array consisting of the values of an array and the number of times each value occurs in an array count() Returns the number of elements in an array or properties of an object sizeof() Returns the size of the array, same as count() The count() and sizeof() Functions The count()[2] and sizeof() functions do the same thing: They both return the number of elements in an array (or properties in an object). To find the number of elements in a multidimensional array, the count() function has an optional mode argument that recursively counts the elements. [2] The sizeof() function is simply an alias for the count() function. Format $number_of_elments =count(array_name); $number_of_elements=count(array_name, 1); $number_of_elements=count(array_name, COUNT_RECURSIVE) Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Example: $bytes=range('a','z'); $size = count( $bytes); // 26 elements $size = sizeof( $bytes); // 26 elements Example 8.18. The count() function Explanation 1 The array called $colors is assigned three values. 2 A new element is added to the $colors array. 3 The count() function returns the number of elements in the array. 4 See Figure 8.22 for the return from the count() function. Figure 8.22. Finding the size of an array. Output from Example 8.18. The array_count_values() Function The array_count_values() function counts how many times a unique value is found in an array. It returns an associative array with the keys representing the unique element of the array, and the value containing the number of times that unique element occurred within the array. Format array array_count_values ( array input ) Example: $hash_count = array_count_values( array("a","b", "a","a")); // Creates an associative array with "a" and "b" as the two keys and // the number of times each occurs in the array (the associated value) Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.