PHP basic study notes (4)

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>

The use 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>
        ——所谓下标，其实就是数组的每一个数据的“顺序号”——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>]  = “<span>444</span><span>”;
        arr2[</span><span>3</span>]  =<span> “abc”;
        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 obtain the length of an array - that is, the number of data in it is:

var v1 = array name.length;

的 Special attention: The maximum bidding of the array is the length of the array decreased by 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 the 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:

V VAR S1 = v5 [0] [1]; // 5 // Equivalent to get the second item of the first item of the V5 array (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(“啦啦啦，我是卖报的小行家，卖报啦卖报啦。”);
}
</span><span>var</span> myDreamGirl =<span> { 
name: “小花”， 
age:</span><span>18</span><span>, 
edu：”大学”,  
sex:”女”,
nengli1: function (){ document.write(“洗衣！”); } ,
nengli2: function (){ document.write(“做饭！”); } ,
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.

v1 as an object has properties and methods:

        Attributes:

                                                                                                                                                                                                .

Method:

On A certain array.concat (other array): connect two arrays into 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 to become 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(“abcdefgabc”);    <span>//</span><span>这是一个“字符串对象”</span>
    <span>var</span> str2 = “abcdefgabc”;                <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——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 );    ——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：”d”</span>
<span>2</span><span>.    str1.toUpperCase();    ——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：”ABCDEFGABC”</span>
<span>3</span><span>.    str1.toLowerCase();    ——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：”abcdefgabc”</span>
<span>4</span><span>.    str1.replace(“字符1”, “字符2”);    ——将str1中的“字符1”替换为“字符2”
</span><span>var</span> s4 = str1.replace(“cd”, “<span>999</span>”);    <span>//</span><span>s4的结果是：”ab999efgabc”</span>
<span>5</span>.    str1.indexOf(“字符1”); ——获得“字符１”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(“ab”);        <span>//</span><span>s5的结果是0</span>
<span>6</span>.    str1.lastIndexOf(““字符1”); ——获得“字符１”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(“ab”);        <span>//</span><span>s6的结果是7</span>
<span>7</span><span>.    str1.substr(n, m )    ——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——注意，这种“取”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：”cdef”</span>
<span>8</span><span>.    str1.substring( n, m )——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：”cd”</span>
<span>9</span><span>.    str1.split(“字符1”)    ——将str1以指定的“字符1”为分界，分割成一个数组，结果是一个数组
</span><span>var</span> s9 = str1.split(“b”);    <span>//</span><span>s9的结果是一个数组：[“a”, “cdefga”, “c”]</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，…..) ——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，…..)     ——求得若干个数值中的最小值。
</span><span>3</span><span>.    Math.abs( 数值1)     ——求得数值1的绝对值
</span><span>4</span><span>.    Math.pow( x，y)        ——求得数值x的y次方，也就是“幂运算”
</span><span>5</span><span>.    Math.sqrt( x )            ——求得x的开方
</span><span>6</span><span>.    Math.round( x )         ——求得x的四舍五入的结果值；
</span><span>7</span><span>.    Math.floor( x )            ——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 )             ——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()        ——获得一个0~<span>1范围中的随机“小数”，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

以上就介绍了php基础学习笔记（4），包括了方面的内容，希望对PHP教程有兴趣的朋友有所帮助。