Detailed introduction to PHP simple syntax_PHP tutorial

PHP simple syntax 1, PHP script code tags

PHP script is the content included in a pair of special tags in the file, such as ASP It is "<%....%>", PHP can be regarded 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 "< ?" php...?>"

In addition, the PHP code block also supports the tag form of .

PHP simple syntax 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 a semicolon.

So, the format of a PHP script can be as follows:

<ol class="dp-xml"><li class="alt"><span><span class="tag"><</span><span> ?php  </span></span></li><li><span>//注意最后一行可以没有分号  </span></li><li class="alt"><span class="tag">?></span><span>   </span></span></li></ol>

PHP Simple Syntax 3, PHP Comments

PHP multi-line comments use ""

Single-line comments use "#" or "//"

PHP simple syntax four, PHP output

In ASP, use "<%=...%>" to quickly output a single line, or use "<%Response.Write("...")%>"

Use "echo()" or "print()" directly in PHP, for example:

<ol class="dp-xml"><li class="alt"><span><span class="tag"><</span><span> ?php  </span></span></li><li><span>echo "a";  </span></li><li class="alt"><span>echo (b);  </span></li><li><span>echo ("c");  </span></li><li class="alt"><span>echo d;  </span></li><li><span class="tag">?></span><span>  </span></span></li></ol>

will output as "abcd", and all four of the above can be output normally.

But this is impossible in ASP, especially echo "a"; and echo d; both output as strings themselves. This requires understanding PHP variable definitions.

PHP simple syntax 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.

<ol class="dp-xml"><li class="alt"><span><span class="tag"><</span><span> ?php  </span></span></li><li><span>$</span><span class="attribute">a</span><span>=</span><span class="attribute-value">"123"</span><span>;  </span></li><li class="alt"><span>echo a;  </span></li><li><span>echo $a;  </span></li><li class="alt"><span class="tag">?></span><span>  </span></span></li></ol>

The input is "a123"

PHP simple syntax 6, the difference between single quotes and double quotes in PHP

<ol class="dp-xml"><li class="alt"><span><span class="tag"><</span><span> ?php  </span></span></li><li><span>$</span><span class="attribute">a</span><span>=</span><span class="attribute-value">"123"</span><span>;  </span></li><li class="alt"><span>echo "$a";  </span></li><li><span>echo '$a';  </span></li><li class="alt"><span class="tag">?></span><span>  </span></span></li></ol>

The output is "123$a", where echo "$a" outputs the value of variable a, and echo '$a' outputs the string itself in single quotes.

<ol class="dp-xml"><li class="alt"><span><span class="tag"><</span><span> ?php  </span></span></li><li><span>$</span><span class="attribute">a</span><span>=</span><span class="attribute-value">"123"</span><span>;  </span></li><li class="alt"><span>echo "$a'$a'";  </span></li><li><span class="tag">?></span><span>   </span></span></li></ol>

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

<ol class="dp-xml"><li class="alt"><span><span class="tag"><</span><span> ?php  </span></span></li><li><span>$</span><span class="attribute">a</span><span>=</span><span class="attribute-value">"123"</span><span>;  </span></li><li class="alt"><span>echo "$a$a";  </span></li><li><span class="tag">?></span><span> </span></span></li></ol>

Another example:

<ol class="dp-xml"><li class="alt"><span><span class="tag"><</span><span> ?php  </span></span></li><li><span>$</span><span class="attribute">a</span><span>=</span><span class="attribute-value">"123"</span><span>;  </span></li><li class="alt"><span>echo "$a$a"";  </span></li><li><span class="tag">?></span><span>  </span></span></li></ol>

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. Definition and use of variables.

3. The usage of single quotes and double quotes.

The above is an introduction to the simple syntax of PHP. I hope it can deepen readers' understanding of the PHP language.

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