Js----- Chapter 4 array

review

loop :

while

Count variables

while( Conditions ){

// The loop body

Count variable update

}

do..while

for

for( Count variables ; Conditions ; Count variable update ){

The loop body

}

1. Feynman method of learning

break: encounter break The loop ends

continue: encounter continue, Then the following code will not be executed , Go straight to the next cycle

break and continue: You can talk to while,do..while,for Use a combination of

1. break and switch Use a combination of

Supplementary cases :

// Loop input 5 Personal scores , If the score is correct, the total score will be output , average 
//  If a score entered is incorrect ( Less than 0 Or greater than 100), Then directly terminate the loop , And output an error prompt , in addition , Cannot output total score and average score .
// Loop input 5 Personal scores , If the score is correct, the total score will be output , average 
            //  If a score entered is incorrect ( Less than 0 Or greater than 100), Then directly terminate the loop , And output an error prompt ,
            // in addition , Cannot output total score and average score .
            
            // Define the summation variable 
            var sum = 0;
            // Define tag variables , Used to record error conditions 
            var flag = false;
​
            //  Loop input 
            for(var i=1;i<=5;i++){
                //  Enter the score 
                var score = Number(prompt(" Please enter the first "+i+" A student's score ",""));
                
                //  If the score is wrong , Then the prompt is wrong , Modify tags , End of cycle 
                if(score<0 || score>100){
                    document.write(" Something went wrong ");
                    flag = true; // Modify tags 
                    break; // End of cycle 
                }
                
                //  Add up the scores 
                sum += score;
            }
            
            if(flag==false){
                //  Output total score average score 
                document.write(" Total score :"+sum+"  average :"+sum/5);
            }

The objectives of this chapter

To define an array

Access assignment of array

Array insertion , Delete , Traverse

Array method

1. Array

1.1 What is an array （ An array is a set of numbers ）

​ Array （Array） yes Orderly The sequence of elements . [1] If a finite number of variables aggregate name , So the name is array name . The variables that make up an array are called the components of the array , Also known as an array of elements , Sometimes it's also called Subscript variable . The number used to distinguish the elements of an array is called the subscript . The array is in Programming in , For convenience , A form of organizing several elements in an orderly form . [1] The collection of these ordered data elements is called an array . An array is a collection of data of the same type .

An array is an ordered sequence of elements :

Each element in the array has its own number Number from 0 Start , To the length of the array minus 1 until , Called subscript .

How to access the data in the array :

Access by subscript , Is to distinguish each data in the array .

 

1.2 Why use arrays

For storing a large amount of data , Arrays can easily open up space in batches , Store batch data , There is no need to define variables one by one .

1.3 General use of arrays

Definition of array

//  Mode one : Create an empty array , No space length 
var  Array name  = new Array(); 
//  Mode two : Create an array with a specified length space 
var  Array name  = new Array( Length number );
//  Mode three : Create an array with some initial values 
var  Array name  = new Array( data 1, data 2, data 3);​
//  Mode 4 :  Use literal quantity "[]", Create an empty array .** Commonly used **
var  Array name  = [];
​//  Methods five :  Use literal quantity "[]", Create an array with initial values  ** Commonly used **
var  Array name  = [ data 1, data 2, data 3...];

Value and assignment of array

Array value ： Array name [ Subscript ];

Array assignment （ modify ）： Array name [ Subscript ] = Value to modify ;

<script type="text/javascript">
	// Common variables : Store one data at a time 
	// Array : Batch data can be stored 
	
	// scene : Store a class 60 One of the js fraction 
	/*var score1 = 78;
	var score2 = 89;
	var score3 = 98;
	....
	var score60 = 76;*/

	// How to create an array 
	// The way 1: var  Array name  = new Array( length ); // The length can be omitted 
	// The way 2: var  Array name  = new Array( data 1, data 2, data 3);// Create data with initial values 
	// The way 3: var  Array name  = []; // Create an empty array literally 

	// The way 1:var  Array name  = new Array( length )
	// Create an empty array 
	//var ary1 = new Array(); 
	// Create a length of 5 The array space of 
	var ary = new Array(5);
	//length: The length of the output array 
	document.write(" length :"+ary.length+"<br/>");
	
	// The assignment of an array : Array name [ Subscript ] =  data 
	ary[0] = 98;
	ary[1] = 33;
	ary[4] = 56;
	// Access the contents of the array 
	document.write(ary[0]+"<br/>");
	document.write(ary[1]+"<br/>");
	document.write(ary[2]+"<br/>");
	document.write(ary[3]+"<br/>");
	document.write(ary[4]+"<br/>");
	document.write("<hr/>");
	document.write(ary[5]); // Array subscript exceeded , No mistake. , Output undefined
	document.write("<hr/>");

	// Use a loop to output the contents of the array 
	//ary.length yes 5：i The change of : 0 1 2 3 4
	for(var i=0;i<ary.length;i++){
		document.write(ary[i]+"<br/>");
	}

  </script>

<script type="text/javascript">
    // var ary = new Array(); // The length is 0 Array of 
	// var ary = new Array(10); // There's only one whole number ,
	//                             Indicates that the array length is 10, At this time, the contents of the array are undefined

	/*
	// Create a length of 4 Array of , The initial data of the array are 10,11,12,13
	var ary = new Array(10,11,12,13);

	// length 
	document.write(" length :"+ary.length+"<br/>");
	document.write(ary[0]+"<br/>");
	document.write(ary[1]+"<br/>");
	document.write(ary[2]+"<br/>");
	document.write(ary[3]+"<br/>");
	*/

	/*
	// Use literals to define empty arrays 
	var ary = [];
	document.write(" length :"+ary.length+"<br/>");
	//js The array of can be dynamically expanded 
	ary[0] = 10;
	ary[1] = 20;
	ary[2] = 30;
	document.write(" length :"+ary.length+"<br/>");
	*/

	// new Date(): Get system time 
	//  The data in the array can store any type 
	var ary = ["abc",100,2.234,new Date()];
	document.write(" length :"+ary.length+"<br/>");
	for(var i=0;i<ary.length;i++){
		// Use    Array name [ Subscript ]  Access each array element 
		document.write(ary[i]+"<br/>")
	}

	document.write("<hr/>");
	// Use for each Output array elements 
	//  among i Is the subscript of an array 
	for(var i in ary){
		alert(i+" : "+ary[i]);
	}


  </script>

Array traversal

Using normal for Loop traversal key exercises

var ary = ["abc",100,2.234,new Date()];
	document.write(" length :"+ary.length+"<br/>");
	for(var i=0;i<ary.length;i++){
		// Use    Array name [ Subscript ]  Access each array element 
		document.write(ary[i]+"<br/>")
	}

Use forEach Traverse

var ary = ["abc",100,2.234,new Date()];
	document.write(" length :"+ary.length+"<br/>");
	// Use for each Output array elements 
	//  among i Is the subscript of an array 
	for(var i in ary){
		alert(i+" : "+ary[i]);
	}

1.4 Array operation

Array search ( Focus on practice )

1. Please enter 5 Results of students , And stored in the array

2. Traversing the array to find the score is 80 Points of , How many students

 

<script type="text/javascript">
	// Define array storage 5 Results of students 
	// And find the first 80 Where is the score in the array 
	// Enter grades :89,56,78,80,98
	//          0  1  2  3  4
	//         76,80,88,87,32
	//          0  1  2  3  4

	// Define the length as 5 Array of 
	var aryScore = new Array(5);
	// Loop input 5 A student's score 
	for(var i=0;i<aryScore.length;i++){
		// Enter your grades 
		var score = Number(prompt(" Please enter the first "+(i+1)+" A student's score :",""));
		// Store scores in an array 
		aryScore[i] = score;
	}

	// Print the array directly 
	//document.write(aryScore);

	// Loop through groups , And determine whether each array element is 80 branch , yes 80 The sub rule displays the corresponding array subscript 
	for(var i=0;i<aryScore.length;i++){
		//alert(aryScore[i]);
		// Traversal array , Judge whether the data currently traversed is 80
		if(aryScore[i]==80){
			alert("80 The subscript of the score is :"+i);
			break;
		}
	}
  </script>

Array insertion

An array is known : var ary = [20,12,33,45,67];

Now enter an arbitrary data , Insert the index into the array as 2 Location

 

<script type="text/javascript">
	// Known array ：20,12,33,45,67
	// The subscript for 2 Insert a data at the position of ( Enter your own )
	var ary = [20,12,33,45,67];
	document.write(ary+"<br/>")

	var num = Number(prompt(" Please enter a data to insert :",""));

	// Use a loop to shift 
	for(var i=ary.length;i>2;i--){
		// Shift the front data in the array to the back 
		ary[i] = ary[i-1];
	}
	// Store the data to be inserted in the subscript 2 On the array space of 
	ary[2] = num;
	document.write(ary);
  </script>

Array deletion

 

Bubble sort

Sort :

• • What is sequencing : From bottom to top , Present in a specific order from high to low
  • Why order : You can get specific data directly by sorting , Improve the utilization efficiency of data

The core of sorting : Comparison and transposition

 

<script type="text/javascript">
	//  Bubble sort 
	//  Data comparison transposition 
	var ary = [56,32,8,76,12,1,3,6,4,5,100,99];
	//         0  1  2  3  4
	document.write(ary+"<br/><hr/>"); //56,32,8,76,12

	// N Bubble order of meta array , Small forward movement compared with two 
	//  The outer layer circulates from 1 beginning , Inner circulation decreases i Go to 

	// Bubble sort 
	for(var i=1;i<ary.length;i++){
		//  Achieved the first round of four comparisons 
		for(var j=0;j<ary.length-i;j++){
			//  Comparison and transposition 
			if(ary[j]>ary[j+1]){
				var temp = ary[j];
				ary[j] = ary[j+1];
				ary[j+1]=temp;
			}
		}
	}
	document.write(ary+"<br/><hr/>"); //
  </script>

1.5  A common method for arrays / function

name	describe
join( Separator )	Convert an array to a string concatenated with a specific delimiter
concat(arr1,arr2)	Merge with another array into a new array
reverse()	Invert array
sort()	Sort the array
push(ele1,ele2)	Add a new element to the end of the array
unshift(ele1,ele2)	Add a new element to the beginning of the array
pop()	Delete the last value in the array Return the deleted value
shift()	Delete the first value in the array Return the deleted value And pop() contrary
splice( Location , Delete the number , The new data ..)	Delete 、 Replace 、 Insert array elements
indexOf(ele)	Find the subscript position of the element

//var ary = [20,10,30,50,60];
    //document.write(ary+"<br/>");
    //  Put the elements in the array , Concatenate the string with the specified symbol 
    //var res = ary.join("----");
    //document.write(res);
    
    //  Invert the array 
    //ary.reverse();
    //document.write(ary);
​
    //var ary2 = [];
    //  Adding elements to an array , Add from the end of the array 
    //ary2.push(100);
    //ary2.push("abc");
    //ary2.push(2.34);
    //document.write(ary2+"<br/>");
​
    //  Delete the value at the end of the array 
    //ary2.pop();
    //document.write(ary2);
​
    //var ary3 = ["aaa","bbb","ccc","ddd","eee"];
    //document.write(ary3+"<br/>")
    //  Use splice Delete the subscript as 2 The elements of 
    //  From the subscript 2 The location of , Delete an element 
    //ary3.splice(2,1);
    //document.write(ary3);
    //  From the subscript 2 The location of , Don't delete elements , But add two new elements 
    //ary3.splice(2,0,"xxx","yyy");
    //document.write(ary3);
    
    //  Find the position of an element in the array 
    //  If we can't find a way back -1
    //alert(ary3.indexOf("ggg"));
​
    var ary4 = [5,3,2,1,4,12,100];
    document.write(ary4+"<br/>");
    //  Sort array elements : Compare the string in character order 
    ary4.sort();
    document.write(ary4);

summary

Definition of array

Assignment and use of arrays

Array operation : Traversal search , Insert , Delete

Common methods of data

example :

Use splice Realize the data insertion of ordered array .

Enter a number through the input box , After inserting the input number into the array, make sure that the array is still in order :

Example : Array [10,50,70,89,99], Enter a number 83, take 83 Insert into the array , After insertion, the array is still in order

​ The array becomes [10,50,70,83,89,99]

 ... Given an ordered array ary
 
 // Defining variables , In the record array , The first location larger than the data to be inserted 
  var pos = -1;
​
  for(var i=0;i<ary.length;i++)
  {
    // Compare the data in the array and the data to be inserted next to each other 
    if(ary[i]>num)
    {
        // When the first data larger than the inserted data is found , Where to record this data , And exit the loop 
        pos = i;
        break;
    }
  }
​
  alert(pos);
​
  // After the cycle , Find the location to insert 
  // Use splice function , Data to be inserted , Insert in the specified location 
  ary.splice(pos,0,num);
  // Output the inserted result 
  document.write(ary);