Sharing some basic knowledge for novices learning PHP_PHP Tutorial

1. PHP script code tags
PHP script is the content included in a pair of special tags in the file. For example, ASP is "<%....%>", PHP can be regarded as It's "".
However, in order to adapt to the XML standard to embed PHP into XML or XHTML, PHP does not recommend using the short form "" and recommends using the long form tag "”
In addition, the PHP code block also supports the tag form of .

2. PHP command delimiter
Each statement in PHP needs to be separated by a semicolon ";", but for the PHP end mark "?>", because It automatically implies a semicolon, so there is no need to append it.
So, the format of a PHP script can be as follows:

3. PHP comments
PHP multi-line comments use "/* ......... */"
Use "#" or "//" for single-line comments

Fourth, PHP output
Use "<%=...%>" in ASP ;"Quickly output a single line, or use "<%Response.Write("...")%>"
Use "echo()" or "print()" directly in PHP, such as:
The output is "abcd", and all the above four types can be output normally.
But this is impossible in ASP, especially when echo "a"; and echo d; are both output as strings themselves. This requires understanding PHP variable definitions.

5. PHP variables
Like ASP, PHP variables can be used directly without defining them first. The type of the variable is automatically generated when assigning a value.
Various variables in PHP are distinguished by adding "$" before the variable name.
The input is "a123"

6. The difference between single quotes and double quotes in PHP
The output is "123$a", among which echo "$a" output The value of variable a is obtained, and echo '$a' outputs the string itself in single quotes.
The output is "123'123'" not "123$a". Although it is '$a', the variable placed under double quotes is still replaced.
So, it can be concluded that as long as the variables are in double quotes, they will be replaced; while those in single quotes will not be replaced.
If the content in double quotes needs to be escaped, use the "" prefix, such as "\", "$", """. So to enter "123$a", it is
Another example:
The output is "123$a"".

Things to note when switching from ASP to PHP:
1. It is easy to forget to write the separator comma ";".
2. Definition and use of variables.
3. The usage of single quotes and double quotes.

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