Skip to content

Quiz: Control Flow, Loops & Array Data Structures

Test your understanding of Loops, nested loops, 2D grids, arrays, and flow control with these review questions.

1. What are the three components separated by semicolons in a standard for loop header for (A; B; C)?

  1. Initialization, Condition, Update (Increment/Decrement)
  2. Condition, Action, Breakpoint
  3. Declaration, Parameter, Return value
  4. Start point, Midpoint, End point
Show Answer

The correct answer is A. A standard for loop header consists of initialization (e.g., let i = 0), condition check (i < 10), and post-iteration update (i++). Options A, C, and D are not the components of a standard for loop header.

Concept Tested: For Loop Construct

2. What dangerous condition occurs if a while loop's condition never evaluates to false?

  1. An infinite loop that freezes the browser tab or main thread
  2. Automatic hardware restart
  3. The loop terminates instantly after one iteration
  4. The canvas switches to 3D WebGL mode
Show Answer

The correct answer is A. If the loop condition never becomes false, the loop executes indefinitely without yielding control back to the browser, blocking the event loop and causing the browser tab to hang. Options B, C, and D are incorrect.

Concept Tested: Infinite Loop Prevention

3. Which loop structure is specifically designed to iterate through row-and-column visual grids on a 2D canvas?

  1. Single while loop with a setTimeout
  2. Nested for loops (an outer loop for y and an inner loop for x)
  3. Recursive draw() invocation
  4. switch statement with 256 cases
Show Answer

The correct answer is B. Nested for loops iterate over columns (x) across every row (y), calculating (x, y) coordinate positions to populate a 2D grid of shapes. Options B, C, and D are unsuitable and inefficient for grid rendering.

Concept Tested: Nested Loops and 2D Grids

4. How do you access the first element of an array named particles in JavaScript?

  1. particles[1]
  2. particles[0]
  3. particles.first()
  4. particles(0)
Show Answer

The correct answer is B. JavaScript arrays are zero-indexed, meaning the first element is at index 0 (particles[0]). particles[1] accesses the second element. Options C and D are invalid syntax in standard JavaScript.

Concept Tested: Array Indexing

5. Which array method adds a new element to the end of an existing array?

  1. pop()
  2. push()
  3. shift()
  4. unshift()
Show Answer

The correct answer is B. push() appends one or more elements to the end of an array. pop() removes from the end, shift() removes from the beginning, and unshift() adds to the beginning.

Concept Tested: Array Push Method

6. Consider the loop: for (let x = 0; x < 100; x += 25). How many total iterations will this loop execute?

  1. 3
  2. 5
  3. 4
  4. 25
Show Answer

The correct answer is C. The loop executes for x = 0, x = 25, x = 50, and x = 75. When x reaches 100, the condition x < 100 evaluates to false, terminating the loop after exactly 4 iterations.

Concept Tested: Loop Step Iteration

  1. Looping backwards executes at 2x hardware speed
  2. JavaScript prohibits forward iteration when calling splice()
  3. Removing an item shifts subsequent index positions left, causing a forward loop to skip the next adjacent element
  4. Backwards loops automatically sort the remaining array elements
Show Answer

The correct answer is C. When an item is removed with splice(i, 1), all subsequent items shift to an index one lower. In a forward loop, i++ advances past the newly shifted item, skipping it. Looping backwards ensures shifted elements have indices already evaluated. Options A, C, and D are false.

Concept Tested: Array Splice in Loops

8. What keyword is used inside a switch statement block to prevent execution from 'falling through' into subsequent cases?

  1. stop
  2. exit
  3. break
  4. return
Show Answer

The correct answer is C. The break keyword terminates the switch statement execution, preventing fall-through into matching subsequent case blocks. Options A, B, and D are not standard case terminators.

Concept Tested: Switch Statement Break

9. A sketch stores 50 particle x-positions in an array xCoords. Which loop header correctly visits every valid element in the array?

  1. for (let i = 0; i <= xCoords.length; i++)
  2. for (let i = 1; i <= xCoords.length; i++)
  3. for (let i = 0; i < 50; i += xCoords)
  4. for (let i = 0; i < xCoords.length; i++)
Show Answer

The correct answer is D. Array indices run from 0 to array.length - 1. The condition i < xCoords.length safely visits every valid index. Option A produces an undefined value on the final iteration because xCoords[length] is out of bounds.

Concept Tested: Array Length Iteration

10. You want to render a 10x10 tile pattern where each tile is 40 pixels wide. Inside nested loops for(let y=0; y<10; y++) and for(let x=0; x<10; x++), what are the pixel coordinates for tile (x, y)?

  1. (x + 40, y + 40)
  2. (x * 10, y * 10)
  3. (x / 40, y / 40)
  4. (x * 40, y * 40)
Show Answer

The correct answer is D. Multiplying the column and row indices by the tile width (x * 40, y * 40) maps discrete grid units (0, 1, 2...) to pixel positions (0, 40, 80...). Option A only adds an offset. Option C divides. Option D scales by grid dimensions rather than tile size.

Concept Tested: Grid Coordinate Scaling