Summary of Xiaopang learning PHP 2-----PHP's b variables and assignment

1. Overview

Although PHP is a weakly typed language, type conversion is still needed sometimes. Let's write about type conversion, variable definition and variable assignment.

1.1 Type conversion

Type conversion in PHP is the same as C language, very simple, just add the type name enclosed in parentheses before the variable.

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2. //Type conversion Description: When using the operator to convert a variable, the original value will not be changed, but when using the settype function to convert, the original value will be changed Value
3. $num = '3.1415926r';
4. echo 'Use the (integer) operator to convert the variable $num type:' . (integer)$num;
5. 'Output the value of variable $num: '. $num; 'Use the settype function to convert the variable $num Type result: '
6. . settype($num,'integer'); echo
7. 'Output the value of variable $num:'. $num; ;
8. ?> The settype() function can convert the specified variable to the specified data type. There are some functions in PHP that can be used to detect whether a variable is of a specified type, such as is_bool() to detect whether it is a Boolean type, is_string() to detect whether it is a string type, etc. 1.2 Define constants Constants can be understood as quantities whose values ​​do not change. After the constant value is defined, it cannot be changed anywhere else in the script. The syntax is: define(constant_name, value, case_sensitive), three The parameters are the name of the constant (required), the value of the constant (required), and whether it is case-sensitive (optional). There are two ways to obtain constants: the first is to obtain them directly by using the variable name; the second is to obtain them through the constant() function. To determine whether a constant has been defined, you can use the defined(stringName) function, which returns true if successful, otherwise false.
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10. //Define constants: define(), get the value of the constant: constant(), determine whether the constant is defined: defined()
11. define( 'count1','Constant value 2'
);

echo count1;

'count1';

echo constant(

$name

).

'
'

1. ; //In fact, this constant of count output
2. echo defined(
3. 'Message'). '
   ';
?>

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2. //Predefined constants
3. echo'Current file path:' . __FILE__. '
   ';
4. echo 'Current number of lines: '; / /82 echo 'Current PHP version information: '
5. . PHP_VERSION. '
   '; echo ' Current operating system: '
6. .PHP_OS; echo'
7. 1.3 Define variables and assign values ​​to variables Unlike many languages, you do not need to declare variables before using them in PHP (you need to declare variables before PHP 4.0), you only need to assign values ​​to variables.
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//Assignment of variables

//The first type: direct assignment of variables, such as $E='ss';
2. //Second: Assignment between variables. Assignment between variables means that the two variables use their own memory after assignment, regardless of interference;​
3. //Third Type: reference assignment. The concept of reference is that when the value of one variable is changed, the other one will also change. Use the & symbol to indicate the reference.
4. //Assignment between variables
5. $string1
=
6. 'spcn'
;
7. $string2
=
8. $string1; $string1
=
9. 'zhuangjia'; 'The value of variable string2 is:'. $string2
.
10. '
    '; .'< ;br>';
11. //Reference assignment $i = 'spcn';
12. $j = & $i; $i = "hello ,$i";
13. echo
14. 'j's value is: '. $j.'
    '
15. ;
16. The value of echo 'i is: '
17. . $i.'
    ';
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    2. //Global variables can be accessed anywhere in the program, but are not available in user-defined functions. If you want to use it, use the global keyword declaration.
    3. $zy = 'won't see';
    4. $zyy = 'will see' ;
    5. function lxt(){
    6. // echo $zy .'
       ';
    7. global $zyy;
    8. echo$zyy.'
       ';
    9. }
    10. lxt();
    ?>
    $trans
    13. = ' you are met';
    14. echo $change_name.
    echo
    15. $$change_name ; //The implementation principle is similar to escape characters, $change_name represents trans, and then adds a $ symbol, that is, the output is $trans
    16. echo '

        '; ?> <

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    //@Operator: Shield error messages
    18. $err = @(5/0);
    echo
    
    

    $err.

    '
    ';

    ?>
    2. / /ternary operator
    3. $value = 100;
    4. $res = ($value == 100) ?'Ternary operation' :
    'No value changed'
    5. ; gt;'
    ;
    7. echo
    8. '

       ';

    9. ?> Function is to write some repeatedly used functions in In an independent code block, call it separately when needed. Create a function syntax: function fun_name($str1,$str2....$strn){}, and then call it with fun_name(XXX).
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        2. //Simple function
        3. function countNumber($num1, $num2){
        4. return"$num1 * $num2 = ".$num1 * $num2.'
           ' ;
        5. }
        6. echo countNumber(10,10);
        7. //Transfer between functions Parameters //Pass by value
        9. functionexample($m
        10. ){ $m
        11. = $ m * 5 + 10; echo
        12. ' The value of $m within the function is: '.$m.'
        13. ; } $mm = 1; example($mm
        14. ); echo
        15. '$m outside the function The value is: '.$mm
        16. .'
            '; ;
        17. //Pass by reference function example1(&
        $m
        18. ){ $m =
        $m
        19. * 5 + 10;
        20. echo
        'The value of $mmm within the function is:'
        21. .$m.'
            ' ;
        22. } $mmm = 1;
        23. example1($mmm); The value of $mmm outside the echo ' function is: '.$mmm.'
            '
        ;
        25. //Optional parameters, where $tax is an optional parameter, you can fill it in or leave it out
        26. function
        values(
        27. $price,$tax =""){ $price
        +=
        28. $tax; 'The price is:'.$ price
        29. .'
            '
        30. ; }
        31. values(100,20); echo '

            ';

        32. //Reference to the function itself &rExample2($tmp
        33. =0){                                                                                                                                         return$tmp; }
        34. $str5 = &example2("kankan");
        35. echo $str5. '

            ';

        36. ?>
        
        

        The above introduces the Xiaopang Learning PHP Summary 2-----PHP's b variables and assignments, including the content. I hope it will be helpful to friends who are interested in PHP tutorials.