Intimate contact with PHP: PHP syntax study notes 1

1. PHP script code tag
PHP script is the content included in a pair of special tags in the file. For example, ASP is "<%....%>", PHP can be seen as "".
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 .
Second, PHP command delimiter
Each statement in PHP needs to be separated by a semicolon ";", but for the PHP end mark "?>", it automatically implies a semicolon, so there is no need to append a semicolon Number.
So, the format of a PHP script can be as follows:
/*
............;
............;
.. .....; Use "/* ......... */" for multi-line comments
Use "#" or "//" for single-line comments
Four, PHP output
Use "<%=...%" in ASP >"Quickly output a single line, or use "<%Response.Write("...")%>"
Use "echo()" or "print()" directly in PHP, such as:
< ?php
echo "a";
echo (b);
echo ("c");
echo d;
?>

will output "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.
$a="123";
echo a;
echo $a;
?>

Input is "a123"
Six, the difference between single quotes and double quotes in PHP
$a="123";
echo "$a";
echo '$a';
?>

The output is "123$a", where echo "$a" outputs the value of variable a, And echo '$a' outputs the string itself in single quotes.
$a="123";
echo "$a'$a'";
?>

Then the output is "123'123'" and 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
$a=" 123";
echo "$a$a";
?>

Another example:
$a="123";
echo "$a$a"\";
?>

The output is "123$a"".
What you need to pay attention to when switching from ASP to PHP:
1. It is easy to forget to write the separator comma ";".
2. The definition and use of variables.
3. The usage of single quotes and double quotes.
The above has introduced the PHP syntax study notes 1 of Intimate Contact with PHP, including the content. I hope it will be helpful to friends who are interested in PHP tutorials.