3. JavaScript WHILE Loops

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Questions and Answers

What happens if the increment statement is forgotten inside a loop?

It results in an infinite loop. (correct)

It will produce an error.

It will execute only once.

The loop will terminate without executing.

In a do...while loop, when is the condition checked?

Before the loop executes.

After the first execution of the body. (correct)

Never checked.

At the end of each execution.

What does the 'break' statement do in a loop?

Stops the execution of the loop immediately. (correct)

Continues with the next iteration.

Pauses the loop for a specified time.

Terminates the entire script.

In a while loop with a true condition, what will happen if there is no break statement?

The loop will execute infinitely. Signup and view all the answers

What is the purpose of the 'continue' statement in a loop?

To skip the current iteration and keep running. Signup and view all the answers

How many iterations does the loop that outputs numbers 0 through 4 make?

5 iterations. Signup and view all the answers

What is the primary difference between a while loop and a do...while loop?

The do...while loop guarantees at least one execution. Signup and view all the answers

In the provided example, what is the output of alert( 'Sum: ' + sum ); when the loop ends?

Sum: The total of all entered numbers Signup and view all the answers

What happens when the increment operator is used after the operand?

The value is increased by one after being returned. Signup and view all the answers

When the decrement operator is applied before the operand, what is the expected outcome?

The value is directly decreased by one and returned. Signup and view all the answers

In a while loop, what is the significance of the condition?

It controls how many times the loop executes. Signup and view all the answers

How does the post-increment operator differ from the pre-increment operator?

The post-increment returns the value before it is incremented. Signup and view all the answers

Which of the following statements about the while loop is accurate?

The condition is evaluated before executing the loop body. Signup and view all the answers

What is the result of the following code? let a = 1; console.log(a++); console.log(a);

1, 2 Signup and view all the answers

If a variable is initialized to 0 and a while loop runs while the variable is less than 5, what happens when the loop exits?

The variable remains equal to 5. Signup and view all the answers

Which statement is true regarding the use of the break and continue statements in loops?

break exits the entire loop, while continue skips the current iteration. Signup and view all the answers

Study Notes

JavaScript Fundamentals (WHILE loops)

JavaScript increment/decrement operators increase or decrease a variable's value by 1.
The ++ operator increments a variable before or after its use.
a++ increments a after its value is used in an expression.
++a increments a before its value is used.
The -- operator decrements a variable before or after its use.
a-- decrements a after its value is used in an expression.
--a decrements a before its value is used.

WHILE Loop

A while loop repeats a block of code as long as a specified condition is true.
The condition is checked before each iteration.
If the condition is initially false, the code block inside the loop is never executed.

Increment and Decrement Operators

Increment/decrement operators in JavaScript add or subtract 1 from an operand
The ++ or -- operators can precede or follow the operand in an expression
When the operators are placed after the operand (postfix), the original value is used in the expression, then the variable is updated.
When the operators are placed before the operand (prefix), the variable is updated first, then the updated value is used in the expression.

Using Increment/Decrement (After/Before the Operand)

Postfix: The original value of the operand is used, then incremented/decremented.
Prefix: The variable is incremented/decremented first, then its new value is used.

WHILE Loop Structure

The while statement creates a loop that executes a specified code block repeatedly as long as a given condition is true.
The condition is evaluated before each execution of the code block.
If the condition becomes false, the loop terminates.

Infinite Loops

Without an increment, a while loop can run indefinitely (infinite loop).
This occurs when the condition that terminates the loop isn't met or is dependent on a variable not modified in the loop's body.
To avoid infinite loops, ensure the condition changes during loop iterations.

Example of a WHILE Loop

let i = 0; (Initializes a counter)
while (i < 5) { (Loop condition: i must be less than 5)
console.log(i); (Prints the current value of i)
i = i + 1; or i++; (Increments i, preventing infinite loop)
} (End of the loop block)

DO...WHILE Loop

The do...while loop executes a code block once, then repeats as long as a specified condition is true.
The condition is checked after each iteration.
The code block in a do...while loop is guaranteed to be executed at least once.

WHILE vs. DO...WHILE

while loops evaluate the condition before each iteration.
do...while loops evaluate the condition after each iteration.

BREAK Statement

The break statement exits the innermost loop immediately.
It's often used in loops that have complex conditions, allowing you to exit the loop early based on specific circumstances.
It's crucial to include a break statement for an infinite loop if you don't want it to run forever: an infinite loop can be beneficial in specific situations but must be stopped.

CONTINUE Statement

The continue statement skips the rest of the current iteration of the loop and proceeds to the next one.
It's used to skip specific parts of a loop's execution.

PHP Examples

PHP also supports while and do...while loops with similar structure to JavaScript.
Key differences include syntax variations and use of echo for output.

Practical Exercises

Practice implementing while loops to solve coding problems and develop your understanding of iteration in programming. Exercises are provided in the linked files in either English or Lithuanian.

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Description

This quiz explores the fundamentals of JavaScript, focusing on WHILE loops and the increment/decrement operators. You will learn how these operators affect variables and gain insights into how WHILE loops work in controlling the flow of code execution. Test your knowledge and reinforce your understanding of these essential programming concepts.