PHP basic study notes (4), PHP basic study notes_PHP tutorial

php basic study notes (4), php basic study notes

Introduction to arrays

Concept: It is a collection of several data put together in a certain order, which is called an "array" as a whole. An array is an ordered collection of data.

Definition form:

<span>var</span>  arr1 = <span>new</span> Array(<span>1</span>,  <span>5</span>,  <span>8</span>,  <span>7</span>,  <span>2</span>,  <span>10</span>);    <span>//</span><span>定义了一个数组，其中具有6个数据</span>
    <span>var</span>  arr2 = <span>new</span> Array();        <span>//</span><span>只是单纯地定义了一个数组（名），但没有给值（数据），即现在是空的</span>
    <span>var</span>  arr3 = [<span>1</span>,  <span>5</span>,  <span>8</span>,  <span>7</span>,  <span>2</span>,  <span>10</span>];    <span>//</span><span>同arr1，只是一种简写的定义法。</span>
    <span>var</span>  arr4 = [ ];        <span>//</span><span>同arr2，也是一个空数组。</span>

Usage of arrays: The so-called use actually refers to the use of each item of the array.

Value:

    <span>var</span>  v1 = arr1[<span>0</span>];    <span>//</span><span>取得数组arr1中的第一项，0叫做下标</span>
        <span>var</span>  v2 = arr3[<span>3</span>] + <span>10</span>;    <span>//</span><span>取得数组arr3中的第4项，4叫做下标</span>
        &mdash;&mdash;所谓下标，其实就是数组的每一个数据的&ldquo;顺序号&rdquo;&mdash;&mdash;从0开始编号，是连续的整数。

Assignment:

                     arr1[0] = 10;

arr2[<span>0</span>]  = <span>22</span><span>;
        arr2[</span><span>1</span>]  = <span>33.3</span><span>;
        arr2[</span><span>2</span>]  = &ldquo;<span>444</span><span>&rdquo;;
        arr2[</span><span>3</span>]  =<span> &ldquo;abc&rdquo;;
        arr2[</span><span>4</span>]  = <span>true</span>;

//At this time, the array arr2 is equivalent to this: [ 22, 33.3, “444”, “abc”, true ]

The "visual image" of the array (taking arr3 as an example):

下标值：    <span>0</span>    <span>1</span>    <span>2</span>    <span>3</span>    <span>4</span>    <span>5</span><span>
数据值：    </span><span>1</span>    <span>5</span>    <span>8</span>    <span>7</span>    <span>2</span>    <span>10</span>

The syntax to get the length of an array - that is, the number of data in it is:

var v1 = array name.length;

Special note: The maximum subscript of an array is the length of the array minus 1.

Usual pattern for array traversal:

var len = array name.length;

for(var i = 0; i < len; i++)

{

//Here is the processing of each item of the array. The writing method of each item is: Array name[i]

}

Another form of array traversal - for in loop statement.

for( var v1 in array name arr1 )

{

//Here is the loop body, which is a traversal loop specifically for array arr1, where the value of v1 is the subscript value representing each item of the array.

//v1 is just a "temporary variable", representing each subscript, which will change from 0 to the maximum subscript of the array.

}

"two-dimensional" array:

<span>var</span>  v1 = [<span>2</span>, <span>5</span>, <span>1</span>, <span>5</span><span>];
</span><span>var</span>  v2 = [<span>5</span>, <span>1</span>, <span>6</span>, <span>8</span><span>];
</span><span>var</span>  v3 = [<span>8</span>, <span>0</span>, <span>9</span>, <span>7</span><span>];
</span><span>var</span>  v4 =<span> [v1,  v2,  v3];
</span><span>var</span>  v5 =<span> [  
[</span><span>2</span>, <span>5</span>, <span>1</span>, <span>5</span><span>], 
[</span><span>5</span>, <span>1</span>, <span>6</span>, <span>8</span><span>], 
[</span><span>8</span>, <span>0</span>, <span>9</span>, <span>7</span><span>]
]; </span>

——There is actually no difference between v4 and v5. Both of them can be called "two-dimensional arrays".

Operations on "two-dimensional" array elements:

Value:

var s1 = v5[0][1]; //5 //Equivalent to getting the second item of the first item in the array v5 (this is still an array).

var s2 = v5[2][3] + 100; //107

Assignment:

v5[0][1] = 200;

v5[2][3] = 300;

Common methods of array objects:

What is a method: A method is actually a function! ——Just if a function "belongs to" an "object", then the function is called a method of the object.

<span>function maibao(){
        document.write(&ldquo;啦啦啦，我是卖报的小行家，卖报啦卖报啦。&rdquo;);
}
</span><span>var</span> myDreamGirl =<span> { 
name: &ldquo;小花&rdquo;， 
age:</span><span>18</span><span>, 
edu：&rdquo;大学&rdquo;,  
sex:&rdquo;女&rdquo;,
nengli1: function (){ document.write(&ldquo;洗衣！&rdquo;); } ,
nengli2: function (){ document.write(&ldquo;做饭！&rdquo;); } ,
nengli3: maibao
};
</span><span>var</span>  v1 = [<span>2</span>, <span>5</span>, <span>1</span>, <span>5</span><span>];
</span><span>var</span>  v2 = [<span>5</span>, <span>1</span>, <span>6</span>, <span>8</span>];

Strictly speaking, an array is also an object - even strings are objects.

As an object, v1 has properties and methods:

Attributes:

An array.length: indicates the length of the array object

Method:

An array.concat (other array): Connect two arrays to form a new "longer" array.
                var s1 = v1.concat( v2 ); //At this time, s1 is an array like this: [2, 5, 1, 5, 5, 1, 6, 8];

                                                

An array.join("string"): "Concatenate" all the items in the array with the specified characters into a "long" string.

var s2 = v1.join(“//”); //The result s2 is the string “2//5//1//5”

某数组.pop(); //将该数组的最后一项“移除”（删除），并返回该项数据，即该数组少了一项

var s3 = v1.pop(); //结果v1只剩这个：[2,5,1]; s3的值是5

某数组.push(新数据项d1); //将新的数据d1添加到该数组的最后位置，即数组多了一项。

var s4 = v1.push( 55 ); //v1此时为：[2,5,1, 55]， s4的值为新数组的长度，即4

某数组.shift(); //将该数组的第一项“移除”（删除），并返回该项数据，即该数组少了一项

var s5 = v1.shift(); //结果v1只剩这个：[5, 1，55]; s5的值是2

某数组.unshift(新数据项d1); //将新的数据d1添加到该数组的最前位置，即数组多了一项。

var v6 = v1.unshift( 66 ); //v1此时为：[66, 5, 1, 55]， s6的值为新数组的长度，即4

javascript语言是一门基于对象的语言。

字符串对象：

<span>var</span> str1 = <span>new</span> String(&ldquo;abcdefgabc&rdquo;);    <span>//</span><span>这是一个&ldquo;字符串对象&rdquo;</span>
    <span>var</span> str2 = &ldquo;abcdefgabc&rdquo;;                <span>//</span><span>这个字符串跟前面str1几乎没有区别</span>
<span>字符串对象的属性：
        .length&mdash;&mdash;获得一个字符串的长度（也就是字符个数）
字符串对象的方法：
</span><span>1</span>.    str1.charAt( n );    &mdash;&mdash;获得字符串str1中位置为n的那个字符（字符的位置也是从０开始算起）<span>var</span> s1 = str1.charAt( <span>3</span> );        <span>//</span><span>s1的结果是：&rdquo;d&rdquo;</span>
<span>2</span><span>.    str1.toUpperCase();    &mdash;&mdash;获取str1全部转换为大写的结果
</span><span>var</span> s2 = str1.toUpperCase();    <span>//</span><span>s2的结果是：&rdquo;ABCDEFGABC&rdquo;</span>
<span>3</span><span>.    str1.toLowerCase();    &mdash;&mdash;获取str1全部转换为小写的结果
</span><span>var</span> s3 = str1.toLowerCase();    <span>//</span><span>s3的结果是：&rdquo;abcdefgabc&rdquo;</span>
<span>4</span><span>.    str1.replace(&ldquo;字符1&rdquo;, &ldquo;字符2&rdquo;);    &mdash;&mdash;将str1中的&ldquo;字符1&rdquo;替换为&ldquo;字符2&rdquo;
</span><span>var</span> s4 = str1.replace(&ldquo;cd&rdquo;, &ldquo;<span>999</span>&rdquo;);    <span>//</span><span>s4的结果是：&rdquo;ab999efgabc&rdquo;</span>
<span>5</span>.    str1.indexOf(&ldquo;字符1&rdquo;); &mdash;&mdash;获得&ldquo;字符１&rdquo;在str1中第一次出现的位置，如果没有出现，结果是-<span>1</span>
<span>var</span> s5 = str1.indexOf(&ldquo;ab&rdquo;);        <span>//</span><span>s5的结果是0</span>
<span>6</span>.    str1.lastIndexOf(&ldquo;&ldquo;字符1&rdquo;); &mdash;&mdash;获得&ldquo;字符１&rdquo;在str1中最后一次出现的位置，如果没有出现，结果是-<span>1</span>
<span>var</span> s6 = str1.lastIndexOf(&ldquo;ab&rdquo;);        <span>//</span><span>s6的结果是7</span>
<span>7</span><span>.    str1.substr(n, m )    &mdash;&mdash;取得str1中从位置n开始的m个字符，m可以省略，则表示从位置n一直取到字符串的最后&mdash;&mdash;注意，这种&ldquo;取&rdquo;并不影响str1这个原始字符
</span><span>var</span> s7 = str1.substr(<span>2</span>, <span>4</span>);    <span>//</span><span>s7为：&rdquo;cdef&rdquo;</span>
<span>8</span><span>.    str1.substring( n, m )&mdash;&mdash;取得str1中从位置n到位置m的前一个字符。
</span><span>var</span> s8 = str1.substring(<span>2</span>, <span>4</span>);    <span>//</span><span>s8为：&rdquo;cd&rdquo;</span>
<span>9</span><span>.    str1.split(&ldquo;字符1&rdquo;)    &mdash;&mdash;将str1以指定的&ldquo;字符1&rdquo;为分界，分割成一个数组，结果是一个数组
</span><span>var</span> s9 = str1.split(&ldquo;b&rdquo;);    <span>//</span><span>s9的结果是一个数组：[&ldquo;a&rdquo;, &ldquo;cdefga&rdquo;, &ldquo;c&rdquo;]</span>

Math对象

Math对象是一个系统内部定义的对象，我们无需去“新建一个Math对象”——跟string对象和array对象不同。即Math对象是直接使用的。

我们学习Math对象，无非是学习一些常见的数学处理函数——这里当就叫做方法了：

属性：

Math.PI——代表圆周率这个“常数”

方法：

<span>1</span><span>.    Math.max(数值1，数值2，&hellip;..) &mdash;&mdash;求得若干个数值中的最大值。
</span><span>2</span><span>.    Math.min(数值1，数值2，&hellip;..)     &mdash;&mdash;求得若干个数值中的最小值。
</span><span>3</span><span>.    Math.abs( 数值1)     &mdash;&mdash;求得数值1的绝对值
</span><span>4</span><span>.    Math.pow( x，y)        &mdash;&mdash;求得数值x的y次方，也就是&ldquo;幂运算&rdquo;
</span><span>5</span><span>.    Math.sqrt( x )            &mdash;&mdash;求得x的开方
</span><span>6</span><span>.    Math.round( x )         &mdash;&mdash;求得x的四舍五入的结果值；
</span><span>7</span><span>.    Math.floor( x )            &mdash;&mdash;求得x的向下取整的结果，即找到不大于x的一个最大的整数。
a)    Math.floor( </span><span>3.1</span> )  <span>3</span><span>
b)    Math.floor( </span><span>3.8</span> )  <span>3</span><span>
c)    Math.floor( </span><span>3</span> )  <span>3</span><span>
d)    Math.floor( </span>-<span>3.1</span> )  -<span>4</span><span>
e)    Math.floor( </span>-<span>3.8</span> )  -<span>4</span>
<span>8</span><span>.    Math.ceil( x )             &mdash;&mdash;求得x的向上取整的结果，即找到不小于x的一个最小的整数
a)    Math.floor( </span><span>3.1</span> )  <span>4</span><span>
b)    Math.floor( </span><span>3.8</span> )  <span>4</span><span>
c)    Math.floor( </span><span>3</span> )  <span>3</span><span>
d)    Math.floor( </span>-<span>3.1</span> )  -<span>3</span><span>
e)    Math.floor( </span>-<span>3.8</span> )  -<span>3</span>
<span>9</span>.    Math.random()        &mdash;&mdash;获得一个0~<span>1范围中的随机&ldquo;小数&rdquo;，含0，但不含1


</span><span>//</span><span>获得两个整数（n1，n2）之间的随机整数的通用做法：</span>
    <span>var</span> v1 =<span> Math.random()
    v1 </span>= v1 * (n2-n1+<span>1</span><span>);
    v1 </span>= Math.floor( v1 ) + n1;    <span>//</span><span>此时v1就是结果
</span><span>//</span><span>将上述3步写出一步就是(通用公式）：</span>
    <span>var</span> v1 = Math.floor( Math.random() * (n2-n1+<span>1</span>) ) + n1

 

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