Add php notes

jaychsu · jaychsu · commit b5f89663ddf3 · 2018-08-02T10:51:51.000+08:00
diff --git a/topic/language/php_syntax.md b/topic/language/php_syntax.md
@@ -0,0 +1,25 @@
+PHP Syntax Note
+======
+
+## General
+
+- A PHP script starts with `<?php` and ends with `?>`. You can also use the shorthand PHP tags, `<?` and `?>`, as long as they're supported by the server.
+- PHP statements end with semicolons `;`.
+- Comment: single-line `//`, multi-line begins with `/*` and ends with `*/`.
+
+## Variable and Constant
+
+`$variable_name = value;`
+`echo $variable_name;`
+
+- A variable name can only contain alpha-numeric characters and underscores. (`A-z`, `0-9`, and `_`)
+- A variable name must start with a letter or an underscore.
+- Variable names are case-sensitive. (`$name` and `$NAME` would be two different variables)
+
+`define(CONSTANT_NAME, value, case-insensitive);`
+`echo CONSTANT_NAME;`
+
+- Constants are similar to variables except that they cannot be changed or undefined after they've been defined.
+- name: Specifies the name of the constant.
+- value: Specifies the value of the constant.
+- case-insensitive: Specifies whether the constant name should be case-insensitive. Default is `false`.
