PHP study notes 1--20110830_PHP tutorial

1. Detailed discussion of Boolean types
​ 1.1 The keywords true and false are not case-sensitive.
 
1.2 In PHP programming, the following situations will be treated as false
* 0 means false, non-0 means true
For example: $a=0;
If($a==false)
                                                             {
                                                                                                                                                                                                              to                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       print("true"); The result is: false
* Decimal 0.0 means false, if the decimal is not 0.0, it is true
* The empty string "" or "0" also means false, otherwise it means true
* null means false
*An array that does not contain any elements also means false
2. Detailed discussion of strings
2.1. A string consists of multiple characters, one character occupies one byte
For example, $a = "abc"; the variable $a occupies three bytes
In 2.2 PHP, there is no theoretical limit to the size of the string, it depends on the size of the memory.
2.3 Two ways to define a string
3.3.1 Single quotes $a='abc';
3.3.1 Double quotes $a="abc";
                                                                                                                                                                                                                                                                   will treat $xxx as a variable when outputting, while ’       will treat $xxx as a string
2.4 The escape character used in "" is
3.Type description of php variables
The conclusion is: the type of PHP variables is not determined by the programmer, but is determined by the context when PHP is executed


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