在数组内部搜索数字

Question

Forgive me, I am not quite skilled and fairly new to the language and programming practices. I am creating a button which prompts the user to enter a number once the number is entered, I create a for loop that iterates through the same amount as the number. For example, the user enters 4 and the screen will display 0 1 2 3 and then I have a button that asks the user to enter a number to see if that number exists in the previous array. So if the user entered 3 it would dispay "it exists" if they entered 5 it would display "number not found". Should I create an array to store the iterations and then run that array through a function that searches for the number. Looking for guidance, thank you for the help guys.

  function getNumber() { var el = document.getElementById("demo"); // Get the user's input and convert it to a number var n = parseInt(prompt("Please enter a number"),10); // Set up a string that will become the output. var output = " "; // loop through given number for(var i = 0; i < n; i++){ // variable containing iterations output += i; //var numArray[i] = output; } //display iterations el.textContent = output; } function findNumber(){ var sn = parseInt(prompt("Search for number"),10); for(var j = 0; j < sn; j++){ } } 

 <button onclick="getNumber()">Click!</button> <p id="demo"></p> <button onclick ="findNumber()">Click!</button> 

Answer 1

Make your n variable global
Than compare if sn is higher than n

 var n; // Make it global function getNumber() { var el = document.getElementById("demo"); // Get the user's input and convert it to a number n = parseInt(prompt("Please enter a number"), 10); // Set up a string that will become the output. var output = " "; // loop through given number for (var i = 0; i < n; i++) { // variable containing iterations output += i; //var numArray[i] = output; } //display iterations el.textContent = output; } function findNumber() { var sn = parseInt(prompt("Search for number"), 10); var isHigher = sn > n; // n is now accessible in this function var message = isHigher ? "Not found" : "Number found!"; alert( message ); } 

 <button onclick="getNumber()">Click!</button> <p id="demo"></p> <button onclick="findNumber()">Click!</button> 

Answer 2

In this theoretic example, it's true that you only need to check if the second number entered is smaller than the first number. If you want to search for a number in an array of any numbers, you can use the javascript indexOf function. See example below:

 var arr = [1,6,77,888]; if (arr.indexOf(66) > -1) { alert('number is in array'); } else { alert('number is not in array'); } 

Answer 3

To search an array, use the indexOf() method of a JavaScript array. The original post gives an example populating the array with myArray[x]=x , creating options pointed out by other solutions. Presuming you want to search a more general case of an array, you could use indexOf directly or define a function that returns true or false :

function inArray(myArray, queryValue) {
    return myArray.indexOf(queryValue) > -1;
};

Arrays in JavaScript are objects with some additional methods like pop() , indexOf() , etc. JavaScript objects are associative arrays; this solution only applies to Array objects. Array objects are constructed with the [] literal or the Array() constructor. Arrays can only have properties named by ints, unlike other JavaScript associative arrays. See Eloquent JavaScript .

Answer 4

There are a couple of ways to do this. For the sake of simplicity, I'll use a global variable here.

 // A global variable to store user input var userInput; function getNumber() { var el = document.getElementById("demo"); // Get the user's input and convert it to a number var n = parseInt(prompt("Please enter a number"),10); // Store the user's input to our global variable userInput = n; // Set up a string that will become the output. var output = " "; // loop through given number for(var i = 0; i < n; i++){ // variable containing iterations output += i; //var numArray[i] = output; } //display iterations el.textContent = output; } function findNumber(){ var el = document.getElementById("result"); var sn = parseInt(prompt("Search for number"),10); // If number is within the range if (sn < userInput) { el.textContent = "it exists"; } // If number is not within the range else { el.textContent = "number not found"; } } 

 <button onclick="getNumber()">Click!</button> <p id="demo"></p> <button onclick ="findNumber()">Click!</button> <p id="result"></p>