3. JavaScript WHILE Loops

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.

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.