PHP Knowledge 2

来源：互联网发布：js判断不等于null 编辑：程序博客网时间：2024/05/22 03:23

字符串数组的默认值为””

””在条件表达式中为flase，非空串为true

数组的下标不能为负数

<HTML>

<HEAD>

<TITLE>一个简单的数组</TITLE>

</HEAD>

/*定义数组$Cities[]*/

$Cities[-1] = "武汉";

//不会报错，但Cities[-1]不能被使用，否则出错

#$Cities[0] = "北京";

$Cities[1] = "天津";

$Cities[2] = "上海";

$Cities[3] = "深圳";

$Cities[100] = "深圳100";

//未被设置的元素默认为""

if($Cities[0] == "")

echo "Cities[0] was not setted and it equal to /"/"/n "; //go here

else

echo "Cities[0] not be setted and it NOT equal to /"/"/n ";

//被设置成””的元素，在条件表达式中为false

if($Cities[0] = "")

echo '$Cities[0] = "" return true ';

else

echo '$Cities[0] = "" return false '; //go here

//被设置成非空串的元素，在条件表达式中为true

if($Cities[0] = "AAA")

echo '$Cities[0] = "AAA" return true '; //go here

else

echo '$Cities[0] = "AAA" return false ';

print("我住在$Cities[500]。 /n");

//打印$Cities[500]，因为未定义初值，因此为””

//print("$Cities[-1]"); //出错数组下标不能小于0

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