PHP学习笔记1-常量，函数
常量：使用const（php5）声明，只能被赋值一次，php5以下版本使用define；
<span style="color: #008080;">1</span> <span style="color: #000000;">php</span><span style="color: #008080;">2</span> <span style="color: #0000ff;">const</span> THE_VALUE = 100;<span style="color: #008000;">//</span><span style="color: #008000;">PHP5中才有const</span><span style="color: #008080;">3</span> <span style="color: #0000ff;">echo</span><span style="color: #000000;"> THE_VALUE;</span><span style="color: #008080;">4</span> <span style="color: #008080;">5</span> <span style="color: #008080;">define</span>('THE_VALUE',200);<span style="color: #008000;">//</span><span style="color: #008000;">低于PHP5的老版本可以使用define</span><span style="color: #008080;">6</span> <span style="color: #0000ff;">echo</span> THE_VALUE;函数：包装了很多功能的代码块；
优点：便于在别处调用
<span style="color: #008080;"> 1</span> <span style="color: #000000;">php</span><span style="color: #008080;"> 2</span> <span style="color: #008080;"> 3</span> <span style="color: #0000ff;">function</span><span style="color: #000000;"> traceHelloPHP(){</span><span style="color: #008080;"> 4</span> <span style="color: #0000ff;">echo</span> 'Hello PHP!'<span style="color: #000000;">;</span><span style="color: #008080;"> 5</span> <span style="color: #0000ff;">echo</span> '<br>'<span style="color: #000000;">;</span><span style="color: #008080;"> 6</span> <span style="color: #0000ff;">echo</span> 'Hello World!'<span style="color: #000000;">;</span><span style="color: #008080;"> 7</span> <span style="color: #0000ff;">echo</span> '<br>'<span style="color: #000000;">;</span><span style="color: #008080;"> 8</span> <span style="color: #000000;">}</span><span style="color: #008080;"> 9</span> <span style="color: #000000;">traceHelloPHP();</span><span style="color: #008080;">10</span> <span style="color: #008080;">11</span> <span style="color: #008000;">//</span><span style="color: #008000;">函数的另外一种执行方式</span><span style="color: #008080;">12</span> <span style="color: #800080;">$func</span> = 'traceHelloPHP';<span style="color: #008000;">//</span><span style="color: #008000;">把函数当成参数传递，e.g.回调方法</span><span style="color: #008080;">13</span> <span style="color: #800080;">$func</span><span style="color: #000000;">();</span><span style="color: #008080;">14</span> <span style="color: #008080;">15</span> <span style="color: #008000;">//</span><span style="color: #008000;">函数的传入参数--单个传入参数</span><span style="color: #008080;">16</span> <span style="color: #0000ff;">function</span> sayHelloTo(<span style="color: #800080;">$name</span><span style="color: #000000;">){</span><span style="color: #008080;">17</span> <span style="color: #0000ff;">echo</span> 'Hello '.<span style="color: #800080;">$name</span>.'<br>'<span style="color: #000000;">;</span><span style="color: #008080;">18</span> <span style="color: #000000;">}</span><span style="color: #008080;">19</span> sayHelloTo('Vito'<span style="color: #000000;">);</span><span style="color: #008080;">20</span> <span style="color: #008080;">21</span> <span style="color: #008000;">//</span><span style="color: #008000;">函数的传入参数--多个传入参数</span><span style="color: #008080;">22</span> <span style="color: #0000ff;">function</span> traceNum(<span style="color: #800080;">$a</span>,<span style="color: #800080;">$b</span><span style="color: #000000;">){</span><span style="color: #008080;">23</span> <span style="color: #008000;">//</span><span style="color: #008000;"> echo 'a = '.$a.', b = '.$b.'<br>';</span><span style="color: #008080;">24</span> <span style="color: #0000ff;">echo</span> "a = <span style="color: #800080;">$a</span>,b = <span style="color: #800080;">$b</span>";<span style="color: #008000;">//</span><span style="color: #008000;">较为简便的写法</span><span style="color: #008080;">25</span> <span style="color: #000000;">}</span><span style="color: #008080;">26</span> traceNum(2,3<span style="color: #000000;">);</span><span style="color: #008080;">27</span> <span style="color: #008080;">28</span> <span style="color: #0000ff;">function</span> add(<span style="color: #800080;">$a</span>,<span style="color: #800080;">$b</span><span style="color: #000000;">){</span><span style="color: #008080;">29</span> <span style="color: #0000ff;">return</span> <span style="color: #800080;">$a</span>+<span style="color: #800080;">$b</span>;<span style="color: #008000;">//</span><span style="color: #008000;">返回值</span><span style="color: #008080;">30</span> <span style="color: #000000;">}</span><span style="color: #008080;">31</span> <span style="color: #0000ff;">echo</span> add(10,2);
