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Delve into the intriguing world of JavaScript programming with a comprehensive guide to understanding the JavaScript Do While Loop. This practical examination of the topic provides a complete walkthrough of the concept, syntax, and examples of implementing a Do While Loop - a fundamental control flow structure in JavaScript. Gain insights into the differences between While and Do While Loop, and deepen your knowledge with advanced techniques, tips and real-world applications. This step-by-step overview is an essential resource for burgeoning coders and seasoned developers seeking a robust grasp on Javascript Do While Loop.
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Jetzt kostenlos anmeldenDelve into the intriguing world of JavaScript programming with a comprehensive guide to understanding the JavaScript Do While Loop. This practical examination of the topic provides a complete walkthrough of the concept, syntax, and examples of implementing a Do While Loop - a fundamental control flow structure in JavaScript. Gain insights into the differences between While and Do While Loop, and deepen your knowledge with advanced techniques, tips and real-world applications. This step-by-step overview is an essential resource for burgeoning coders and seasoned developers seeking a robust grasp on Javascript Do While Loop.
A Javascript Do While Loop is an important control structure in Javascript, which is used to repeat a block of code until a certain condition becomes false. Unlike other loop forms, it does not evaluate the condition before running the loop. Instead, it will execute the code block at least once before checking the condition.
In Javascript, the Do While Loop is unique due to its 'post-test' loop nature. This means that the test condition, which controls the loop, is evaluated after the loop has been executed. The loop will always run at least once, regardless of the test condition. This is a contrast to a standard 'while loop' or 'for loop', which are 'pre-test' loops where the condition is tested before the loop is run.
Here's an example that illustrates the functioning of a do while loop.
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do {
statement(s);
} while (condition);
Implying, that the 'statement(s)' is/are executed first, and then the 'condition' is evaluated. If the 'condition' is true, then the loop is executed again, and this continues until the 'condition' is false.
| Keyword 'do' | This keyword begins the do while loop structure. It is followed by the block of code within curly brackets { } |
| Block of code | This is the segment of code that is to be repeatedly executed by the loop. It is enclosed within curly brackets { } |
| Keyword 'while' | This keyword signifies the start of the condition expression. It is followed by a specific condition enclosed within parentheses ( ) |
| Condition | This is the test condition which is evaluated after each iteration of the loop. If it's true the loop continues, else it halts. |
For Instance,
let i = 0;
do{
console.log(i);
i++;
}while(i < 5);
In this example, Javascript Do While loop will print numbers 0 to 4. Firstly, 'i' is initialized to 0. The loop will run and print the value of 'i'. Then, 'i' is incremented by 1. This continues till 'i' is less than 5, post which the loop will terminate.
let counter = 1;
do {
console.log(counter);
counter++;
} while (counter <= 5);
In the given example, the variable 'counter' begins with the value of 1. During each passing of the loop, the value is printed and then incremented by 1. This cycle continues until the counter exceeds 5.
Secondly, consider a more complicated scenario involving an array and a do while loop.
let arrayExample = [ 'apple', 'banana', 'cherry' ];
let i = 0;
do {
console.log(arrayExample[i]);
i++;
} while (i < arrayExample.length);
In this case, the variable 'i' acts as the index for the array. Starting from 0, the script prints the value at the current index, before incrementing the index by 1. This cycle repeats until 'i' no longer falls within the array's length.
let countUpToHundred = 1;
do {
console.log(countUpToHundred);
countUpToHundred++;
} while (countUpToHundred <= 100);
In another example, suppose a programme requiring user input until it receives a valid value. The do while loop would be an apt choice, as it guarantees execution of the statement at least once, thereby seeking input before proceeding.
let userInput;
do {
userInput = prompt("Enter a valid number!");
} while (isNaN(userInput));
Lastly, consider a complex scenario that emulates a guessing game. In this game, the aim is to guess the correct number. A Do While loop can ensure the game continues until the correct guess is made.
let correctNumber = 7, guessedNumber;
do {
guessedNumber = prompt("Guess the number!");
} while (guessedNumber != correctNumber);
In these use-cases, the utility of Javascript Do While Loop becomes clear. While its usage can vary in complexity, the core remains intact - execute the code block once, and continue until the while condition evaluates to false.
let i = 0;
do{
console.log(i);
// A mistake: i is not being incremented, causing an infinite loop.
}while(i < 5);
let outerLoop = 0;
do{
let innerLoop = 0;
do{
console.log(outerLoop, innerLoop);
innerLoop ++;
}while(innerLoop < 5);
outerLoop++;
}while(outerLoop < 5);
let arrayExample = [ 'apple', 'banana', 'cherry', 'date', 'elderberry' ];
let i = 0;
do {
if(arrayExample[i] == 'cherry') {
alert('Found the cherry!');
break; // Loop exits here
}
i++;
} while (i < arrayExample.length);
while (condition){
// Code to be executed
}
Conversely, the **Do While loop** follows a 'post-test' loop scheme. This means that the loop's code block will be manoeuvred once before the condition is evaluated. Hence, regardless of whether the condition is true or false, the code block inside a Do While loop will always run at least once.
do {
// Code to execute
} while (condition);
To illustrate this difference:
let i = 5;
while (i < 5) {
console.log(i);
i++;
}
The While loop will not run the code block because the condition i < 5 is false at the outset. Nothing will be printed to the console in this scenario.
Now we will use a similar code block and condition, but within a Do While loop:
let i = 5;
do {
console.log(i);
i++;
} while (i < 5);
Although the condition i < 5 is false when the loop starts, the console will print the number 5 once. This is because the Do While loop will always run its code block once, before the condition is checked.
In terms of syntax, both structures are similar but have a slight difference as seen in their respective code structures shared above. Syntax isn't usually a decider when choosing between them. The significant deciding factor is often the requirement of whether the code block should run at least once, or ought to check the condition prior to the first execution.
To summarise these differences:
| Aspect | While Loop | Do While Loop |
| Initial Check | The condition is check before first execution. | The loop executes once before checking the condition. |
| Execution | Execution occurs only if the condition is true. | Execution happens at least once, irrespective of the condition. |
| Syntax | Condition appears before the code block. | Condition appears after the code block. |
A Data structure is a specialised format for organising and storing data.
var myArray = [1, 2, 3, 4, 5];
var i = 0;
do {
myArray[i] *= 2;
i++;
} while (i < myArray.length);
In this example, the loop iterates over the elements of 'myArray', doubling the value of each element.
It's also possible to use a Do While Loop for iterating through linked lists. Linked lists are unique data structures in which elements point to the next element in the list, often used in more complex data manipulation tasks.
var currentNode = headNode;
do {
console.log(currentNode.value);
currentNode = currentNode.next;
} while (currentNode !== null);
In this script, each node in the linked list is accessed and its value logged to the console.
Another robust use case of Do While Loop is in **interactive user processes**. The loop can be used to repeat a prompt until the user provides satisfactory input.
do {
var userAge = prompt('Please enter your age');
} while (isNaN(userAge));
In the interactive user process script, the prompt repeats until the user inputs a number, demonstrating a common use case in web development or any other user-oriented applications.
From manipulating complex data structures such as arrays and linked lists, to designing user-friendly interactive processes, the Do While Loop plays a major role in Javascript programming.
let x = 0;
do {
let y = 0;
do {
loadImage.pixel(x, y);
y++;
} while (y < loadImage.height);
x++;
} while (x < loadImage.width);
In this fragment of code, the outer loop navigates through the rows, while the inner loop scans individual pixels in each row, applying the 'loadImage.pixel()' method.
Consider as well the role of Do While Loops in **file system tasks**. When managing file inputs or outputs, the Do While Loop becomes a formidable tool for reading input streams or writing to output streams.
let dataChunk;
do {
dataChunk = fileInputStream.read();
if (dataChunk !== null) {
console.log(`Read data: ${dataChunk}`);
}
} while (dataChunk !== null);
The above script utilises the Do While Loop to read data from a file input stream and print it to the console. The loop will continue as long as there is data to read.
Whether manipulating complex data in mathematical and computational applications, implementing highly interactive user interfaces, or supporting advanced file I/O operations, the Do While Loop is a versatile instrument in JavaScript, fit for real-world programming applications. Its flexibility makes it a bedrock construct in the coder's toolkit.YOUR SCORE
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SIGNUP SIGNUPFlashcards in Javascript Do While Loop15
Start learningWhat is the unique feature of a Javascript Do While Loop?
The unique feature of a Javascript Do While Loop is its 'post-test' nature, which means it executes the code block at least once before checking the condition.
What are the primary components of Javascript Do While Loop's syntax?
The primary components of Javascript Do While Loop's syntax are the 'do' keyword, a block of code, the 'while' keyword, and a condition to evaluate.
How does a Javascript Do While Loop function?
A Javascript Do While Loop executes a block of code once, then checks a condition. If the condition is true, the loop is executed again. This continues until the condition is false.
What is the structure of a basic Do While Loop in Javascript by showcasing a counting example from 1 to 5?
A Javascript Do While loop has a structure where a variable 'counter' begins with a value. This value is printed, incremented by 1 and continues in a cycle until the said condition is no longer met. The given example is a simple counter from 1 to 5.
How is a Do While Loop in Javascript applied in an example involving an array?
A variable 'i' is used as an index for the array. Starting from 0, the script prints the value at the current index then increments the index by 1. This cycle occurs until 'i' no longer falls within the array's length.
What is a practical usage of Do While Loop in Javascript for a guessing game scenario?
The aim of the guessing game is to guess the correct number. A Do While Loop can ensure that the game continues until the correct guess is made.
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