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Articles on Trending Technologies
Technical articles with clear explanations and examples
Is it legal to recurse into main() in C++?
In C or C++, the main function is like other functions. So we can use the functionalities that are present in some other functions, also in the main function.In the following program, we will see how the main() is using recursively to print some numbers in reverse order.Example Code#include using namespace std; int main () { static int x = 10; cout
Read MoreMongoDB order by two fields sum?
To order by two fields sum, you can use the aggregate framework. Let us first create a collection with documents> db.orderByTwoFieldsDemo.insertOne({"Value1":10, "Value2":35}); { "acknowledged" : true, "insertedId" : ObjectId("5ca285576304881c5ce84baa") } > db.orderByTwoFieldsDemo.insertOne({"Value1":12, "Value2":5}); { "acknowledged" : true, "insertedId" : ObjectId("5ca2855f6304881c5ce84bab") } > db.orderByTwoFieldsDemo.insertOne({"Value1":55, "Value2":65}); { "acknowledged" : true, "insertedId" : ObjectId("5ca285686304881c5ce84bac") }Following is the query to display all documents from a collection with the help of find() method> db.orderByTwoFieldsDemo.find().pretty();This will produce the following output{ "_id" : ObjectId("5ca285576304881c5ce84baa"), "Value1" : 10, "Value2" : 35 } { "_id" : ObjectId("5ca2855f6304881c5ce84bab"), "Value1" ...
Read MoreHow to convert Long array list to long array in Java?
Firstly, declare a Long array list and add some elements to it:ArrayList < Long > arrList = new ArrayList < Long > (); arrList.add(100000 L); arrList.add(200000 L); arrList.add(300000 L); arrList.add(400000 L); arrList.add(500000 L);Now, set the same size for the newly created long array:final long[] arr = new long[arrList.size()]; int index = 0;Each and every element of the Long array list is assigned to the long array:for (final Long value : arrList) { arr[index++] = value; }Exampleimport java.util.ArrayList; public class Demo { public static void main(String[] args) { ArrayList
Read MoreHow to count null values in MySQL?
To count null values in MySQL, you can use CASE statement. Let us first see an example and create a table −mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, FirstName varchar(20) ); Query OK, 0 rows affected (0.77 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(FirstName) values('John'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable(FirstName) values(null); Query OK, 1 row affected (0.25 sec) mysql> insert into DemoTable(FirstName) values(''); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable(FirstName) values('Larry'); Query OK, 1 row affected (0.17 ...
Read MoreHow to convert MySQL null to 0 using COALESCE() function?
You can use the COALESCE() function to convert MySQL null to 0SELECT COALESCE(yourColumnName, 0) AS anyAliasName FROM yourTableName;Let us first create a table. The query to create a table is as followsmysql> create table convertNullToZeroDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(20), -> Salary int -> ); Query OK, 0 rows affected (1.28 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into convertNullToZeroDemo(Name, Salary) values('John', NULL); Query OK, 1 row affected (0.20 sec) mysql> insert into convertNullToZeroDemo(Name, Salary) values('Carol', 5610); Query OK, 1 ...
Read MoreRandom number generation in C++
Let us see how to generate random numbers using C++. Here we are generating a random number in range 0 to some value. (In this program the max value is 100).To perform this operation we are using the srand() function. This is in the C library. The function void srand(unsigned int seed) seeds the random number generator used by the function rand.The declaration of srand() is like below:void srand(unsigned int seed)It takes a parameter called seed. This is an integer value to be used as seed by the pseudo-random number generator algorithm. This function returns nothing.To get the number we ...
Read MoreFinding highest value from sub-arrays in MongoDB documents?
To find the highest value from sub-arrays in documents, you can use an aggregate framework. Let us first create a collection with documents> db.findHighestValueDemo.insertOne( ... { ... _id: 10001, ... "StudentDetails": [ ... { "StudentName": "Chris", "StudentMathScore": 56}, ... { "StudentName": "Robert", "StudentMathScore":47 }, ... { "StudentName": "John", "StudentMathScore": 98 }] ... } ... ); { "acknowledged" : true, "insertedId" : 10001 } > db.findHighestValueDemo.insertOne( ... { ... _id: 10002, ... "StudentDetails": [ ...
Read MoreJava Program to convert mathematical string to int
To evaluate mathematical string to int, use Nashorn JavaScript in Java i.e. scripting. Nashorn invoke dynamics feature, introduced in Java 7 to improve performance.For scripting, use the ScriptEngineManager class for the engine:ScriptEngineManager scriptEngineManager = new ScriptEngineManager(); ScriptEngine scriptEngine = scriptEngineManager.getEngineByName("nashorn");Now, use put() to set a key/value pair in the state of the ScriptEngine:scriptEngine.put("one", 10); scriptEngine.put("two", 50); scriptEngine.put("three", 40);Now, here is the mathematical string. Use eval to evaluate:String strExp = "(one + two - three) == 20"; Object evalExp = scriptEngine.eval(strExp);Exampleimport javax.script.ScriptEngine; import javax.script.ScriptEngineManager; import javax.script.ScriptException; public class Demo { public static void main(String[] args) { ScriptEngineManager ...
Read MoreC program to write an image in PGM format
The PGM is the Portable Gray Map. If we want to store a 2d array in C as images in PNG, JPEG, or any other image format, we have to do lots of work to encode the data in some specified format before writing into a file.The Netpbm format gives an easy and portable solution. The Netpbm is an open source package of graphics program and it is used basically in linux or Unix platform. It also works under Microsoft Windows systems.Each file starts with a two-byte magic number. This magic number is used to identify the type of the ...
Read MoreHow to print list values in reverse order using Collections.reverse() in Android?
This example demonstrates How to print list values in reverse order using Collections.reverse() in Android.Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.Step 2 − Add the following code to res/layout/activity_main.xml. In the above code, we have taken name and record number as Edit text, when user click on save button it will store the data into arraylist. Click on refresh button to get the ...
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