Use JS+PHP to display the maximum value after entering numbers-PHP Tutorial-php.cn

This article mainly introduces JS+PHP to realize the display of the maximum value and the relative position of the number after the user inputs the number. The article provides detailed sample code for your reference and study. Friends who need it are below Let’s take a look together.

This article mainly introduces to you the relevant content about JS+PHP realizing that the maximum value and location are displayed after the user enters a number. The purpose is to distinguish the difference between JS and PHP and broaden your thinking. Let’s take a look at the details together. Introduction:

Analysis

## 1. Use JS prompt to enter the value that the user wants to enter.

2. Use the text tag of the HTML form to pass the input value to the PHP processing file

3.PHP performs numerical judgment and selects the maximum value and position.

From shallow to deep :

1. Get the maximum value of the array in JS.

var a=[10,20,40,30];
 // var max=0;
 var max=a[0];
 for(var i=0;i<a.length;i++){
 if(max<a[i]){
  max=a[i];
 }
 }
 alert("最大数为"+max);

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It’s worth noting here Yes: You cannot directly set a variable max=0, because you are not sure whether the number you enter in the future is less than 0 or greater than 0 [the case is greater than 0], so you should choose a number in the array, just the first number in the array A good one

max=a[0] .

Because the JS language is based on object-oriented process, everything in JS can be an object, so its array has attributes, length is an attribute of JS array that is used to obtain the length of the array. With this attribute, you can traverse the array and compare them one by one.

2. Get the maximum and minimum values of the array and their values in JS The position (that is, the number in the array)

[Note: The position in this case is +1 for the convenience of viewing, and the beginning of the JS array is also 0]

var a=[10,20,40,30];
 var max=a[0];//不能指定一个数为最大值[var max=0](除非是确定的情况下),应该用数组里面的值,a[0]即让数组第一个值作为比较的最大值.
 var maxaddress=0;
 var min=a[0];
 var minaddress=0;
 for(var i=0;i<a.length;i++){
  if(max<a[i]){
   max=a[i];
   maxaddress=i
  }
  if(min>a[i]){
   min=a[i];
   minaddress=i
  }
 }
 alert("最大数为"+max+"位置为第"+(maxaddress+1)+"个");
 alert("最小数为"+min+"位置为第"+(minaddress+1)+"个");

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3. Now use prompt for user input to obtain the value to find the maximum value, etc.

Difficulty:

1. How to input, Use prompt

2. How to convert a string into an array and convert the format?

Prerequisite knowledge:

1. What is used to split the string is The split method of the JS string object (note that everything in JS is an object, so it is called a method, not a function)

2. How to convert an "abc" string into a number type.

字符串转数字类型

◆Number

★数字类型的字符串，转换之后得到的数字。var n1="123"; var n2=Number(n1);//123

★★非数字字符串，转换之后得到是NaN。var n1="123abc"; var n2=Number(n1);//Nan 

★小数类型的字符串，转换之后得到的是原数字。var n1="123.23"; var n2=Number(n1);//123.23

 

◆parseInt

★整数数字类型的字符串，转换之后得到的整数数字。var n1="123"; var n2=parseInt(n1);//123

★数字开头的字符串，转换之后得到的是前边的数字。var n1="123abc"; var n2=parseInt(n1);//123

★非数字开头的字符串，转换之后得到的是NaN。。var n1="abc123"; var n2=parseInt(n1);//NaN

★★小数类型的字符串，转换之后取整(小数点直接省略)。var n1="123.53"; var n2=parseInt(n1);//123 var n1="-5.93"; var n2=parseInt(n1);//-5

 

◆parseFloat

★整数数字类型的字符串，转换之后得到的整数数字。var n1="123"; var n2=parseFloat(n1);//123

★数字开头的字符串，转换之后得到的是前边的数字。var n1="123abc"; var n2=parseFloat(n1);//123

★非数字开头的字符串，转换之后得到的是NaN。var n1="abc123"; var n2=parseFloat(n1);//NaN

★★小数类型的字符串，转换之后得到的是原数字。var n1="123.23"; var n2=parseFloat(n1);//123.23

 

转布尔类型

★数字和字符串转完之后为true。

★undefined、null、0转完之后为false.

var n1=123; var n2=Boolean(n1);//true

var n1="123"; var n2=Boolean(n1);//true

var n1="0"; var n2=Boolean(n1);alert(n2);//true

var n1; var n2=Boolean(n1);//false

var n1=null; var n2=Boolean(n1);//false

var n1=0; var n2=Boolean(n1);//false

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After the above analysis is completed, start writing code

<script>
  //var a=new Array(-12,34,56,88,32,"aa","-34.33","-34.34",12.23);
  /*var a=new Array(prompt("请输入数字"));
  document.write(a);*/
  var b=prompt("请输入要比较的数,用\",\"号隔开");
  var a=new Array();
  a=b.split(",");
  // for(var j=0;j<a.length;j++){
  //   document.write(a[j]);
  // }
  alert(typeof(a)+" JS数组本质是对象啊!!");//本质是对象 PHP数组就是数组,没有属性(比如length)
  document.write(a+"<br>");
  console.log(a+"<br>");
  var max=parseFloat(a[0]);
  //document.write(max);
  var maxaddress=0;
  var min=parseFloat(a[0]);
  var minaddress=0;
  
  for(var i=0;i<=a.length;i++){
   var shu=parseFloat(a[i]);
   if(shu>max){
    max=shu;
    maxaddress=i;
   }
   if(shu<min){
    min=a[i];
    minaddress=i;
   }
  }
  document.write("最大数为"+max+"位置为第"+(maxaddress+1)+"个"+"<br>");
  document.write("最小数为"+min+"位置为第"+(minaddress+1)+"个");
 </script>

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4. The above is processed by JS, my purpose It is to link JS+PHP+HTML.

PHP cannot directly interact with the front end, that is, it cannot directly obtain the value entered by the user, but must pass the html form

To transfer JS data to PHP, you can use AJAX, but I will talk about it later. Let’s see what methods are available today.

1. Make an HTML form:

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>Document</title>
 
</head>
<body>
 <form action="deal.php" method="post">
 请输入数字:<input type="text" id="shu" name="shuzi" value="">
 <input type="submit" value="提交">
 </form>
 
</body>
</html>

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2. JS passes value to HTML:

 <script type="text/javascript">
  var a=prompt("请输入数字");
  document.getElementById("shu").value=a;
 </script>

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There is a pitfall here. If you write JS code in the header of HTML, an error will be reported, saying

Uncaught TypeError: Cannot set property 'value' of null

Because of the browser parsing order, when the browser parses JS (when entering the number is completed), the browser starts parsing HTML, although JS assigns a value The value of text is NULL when parsed later by HTML. This is contradictory.

So try to write the JS code at the back as much as possible. You parse the HTML first, and then I will Give you the value. (Detailed analysis of the specific situation, not necessarily all JS code is in the header)

5. Okay, HTML has passed the value, now look at PHP

<?php
header("Content-type:text/html;charset=utf-8");
$a=$_POST[&#39;shuzi&#39;];
//var_dump($a);
$b=explode(&#39;,&#39;,$a);
for($i=0;$i<count($b);$i++){
 echo $b[$i];
}
var_dump($b);

$max=$b[0];
$maxaddress=0;
for($j=0;$j<count($b);$j++){
 if($b[$j]>$max){
  $max=$b[$j];
  $maxaddress=$j;
 }

}
echo "最大值是".$max."<br>";
echo "位置为第".($maxaddress+1)."个";


?>

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Here we mainly look at explode (split the string into arrays) count (get the number of arrays)

Also pay attention to the type conversion problem, we will add it later or write it yourself.

Last picture above:

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