Episode 7 — DSA with JavaScript / 7.2 — Loops Nested Loops Pattern Programming

7.2 — Interview Questions: Loops, Nested Loops & Patterns

<< Overview

Beginner

Q1. What is the difference between for, while, and do-while loops?

Answer:

Featureforwhiledo-while
Structureinit; condition; updatecondition onlycondition at end
Min executions001
Best forKnown countUnknown countRun-at-least-once
// for: known count
for (let i = 0; i < 5; i++) console.log(i);

// while: unknown count
while (data.hasNext()) process(data.next());

// do-while: at least once
do { choice = getInput(); } while (choice !== "quit");

Q2. What is an infinite loop? How can it happen accidentally?

Answer: An infinite loop never terminates because its condition never becomes false.

Common causes:

  1. Forgetting to update the loop variable
  2. Wrong increment direction (++ instead of --)
  3. Floating-point comparison that never equals exactly
  4. Condition that can never be false
// BUG: i never changes
let i = 0;
while (i < 10) { console.log(i); } // infinite!

// FIX:
while (i < 10) { console.log(i); i++; }

Q3. How does break differ from continue?

Answer:

  • break: Exits the loop entirely
  • continue: Skips the rest of the current iteration, goes to next
for (let i = 0; i < 5; i++) {
    if (i === 2) continue;  // skip 2
    if (i === 4) break;     // exit at 4
    console.log(i);
}
// Output: 0, 1, 3

Q4. Write code to print a right-angled triangle of height n.

Answer:

function rightTriangle(n) {
    for (let i = 1; i <= n; i++) {
        console.log("*".repeat(i));
    }
}

void rightTriangle(int n) {
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j < i; j++) cout << "*";
        cout << endl;
    }
}

Q5. How do you iterate over an array in JavaScript vs C++?

Answer:

const arr = [10, 20, 30];

// for loop
for (let i = 0; i < arr.length; i++) { ... }

// for...of
for (const val of arr) { ... }

// forEach
arr.forEach((val, i) => { ... });

vector<int> arr = {10, 20, 30};

// Index-based
for (int i = 0; i < arr.size(); i++) { ... }

// Range-based
for (int val : arr) { ... }

// Iterator
for (auto it = arr.begin(); it != arr.end(); ++it) { ... }

Intermediate

Q6. How do you print a centered pyramid of stars?

Answer: Row i (0-indexed) needs (n-1-i) spaces followed by (2i+1) stars.

function pyramid(n) {
    for (let i = 0; i < n; i++) {
        console.log(" ".repeat(n-1-i) + "*".repeat(2*i+1));
    }
}

Dry-run for n=4:

Row 0: "   *"     (3 spaces, 1 star)
Row 1: "  ***"    (2 spaces, 3 stars)
Row 2: " *****"   (1 space,  5 stars)
Row 3: "*******"  (0 spaces, 7 stars)

Q7. What is the time complexity of printing an n×n pattern?

Answer: O(n²) — the outer loop runs n times, and for each iteration, the inner loop runs up to n times (or proportional to n). Total operations are proportional to n × n = n².

For a triangular pattern (1+2+3+...+n stars), the total is n(n+1)/2, which is still O(n²).

Q8. Print Pascal's triangle. Explain the algorithm.

Answer: Each element is C(i,j) = i! / (j! × (i-j)!). We can compute it incrementally:

function pascal(n) {
    for (let i = 0; i < n; i++) {
        let val = 1;
        let row = " ".repeat(n - 1 - i);
        for (let j = 0; j <= i; j++) {
            row += val + " ";
            val = val * (i - j) / (j + 1);
        }
        console.log(row);
    }
}

Dry-run for n=5:

    1
   1 1
  1 2 1
 1 3 3 1
1 4 6 4 1

Q9. How would you optimize a nested loop that searches for a pair with a given sum?

Answer:

// Brute force: O(n²)
function pairSum(arr, target) {
    for (let i = 0; i < arr.length; i++) {
        for (let j = i + 1; j < arr.length; j++) {
            if (arr[i] + arr[j] === target) return [i, j];
        }
    }
    return null;
}

// Optimized with hash map: O(n)
function pairSum(arr, target) {
    const seen = new Map();
    for (let i = 0; i < arr.length; i++) {
        const complement = target - arr[i];
        if (seen.has(complement)) return [seen.get(complement), i];
        seen.set(arr[i], i);
    }
    return null;
}

The hash map approach replaces the inner loop with an O(1) lookup.

Q10. Print a diamond pattern. Explain the symmetry.

Answer: A diamond of height 2n-1 is a pyramid (n rows) followed by an inverted pyramid (n-1 rows).

function diamond(n) {
    for (let i = 0; i < n; i++) {
        console.log(" ".repeat(n-1-i) + "*".repeat(2*i+1));
    }
    for (let i = n-2; i >= 0; i--) {
        console.log(" ".repeat(n-1-i) + "*".repeat(2*i+1));
    }
}

Advanced

Q11. Explain labeled loops. When are they useful?

Answer: Labels allow break or continue to target an outer loop from within an inner loop. They're useful for 2D searches where you need to exit both loops.

search:
for (let i = 0; i < matrix.length; i++) {
    for (let j = 0; j < matrix[i].length; j++) {
        if (matrix[i][j] === target) {
            console.log(`Found at (${i}, ${j})`);
            break search;  // exits outer loop
        }
    }
}

C++ alternative: Use a boolean flag or return from a function.

Q12. How do you avoid O(n²) when working with nested data?

Answer: Common strategies:

  1. Hash maps — Replace inner loop with O(1) lookup
  2. Sorting + two pointers — O(n log n) instead of O(n²)
  3. Prefix sums — Pre-compute cumulative sums
  4. Early termination — Break as soon as answer is found
  5. Space-time tradeoff — Cache results to avoid recomputation

Q13. Implement Floyd's triangle. What is the pattern?

Answer: Floyd's triangle fills rows with consecutive natural numbers:

1
2 3
4 5 6
7 8 9 10

function floyds(n) {
    let num = 1;
    for (let i = 1; i <= n; i++) {
        let row = "";
        for (let j = 0; j < i; j++) {
            row += (num++) + " ";
        }
        console.log(row.trim());
    }
}

The total numbers printed is n(n+1)/2 (triangular number).

Q14. Write a spiral matrix printer.

Answer:

function spiralOrder(matrix) {
    const result = [];
    let top = 0, bottom = matrix.length - 1;
    let left = 0, right = matrix[0].length - 1;

    while (top <= bottom && left <= right) {
        for (let i = left; i <= right; i++) result.push(matrix[top][i]);
        top++;
        for (let i = top; i <= bottom; i++) result.push(matrix[i][right]);
        right--;
        if (top <= bottom) {
            for (let i = right; i >= left; i--) result.push(matrix[bottom][i]);
            bottom--;
        }
        if (left <= right) {
            for (let i = bottom; i >= top; i--) result.push(matrix[i][left]);
            left++;
        }
    }
    return result;
}

Time: O(m×n) | Space: O(1) excluding output

Quick-fire table

#QuestionAnswer
1Loop that runs body first?do-while
2Exit inner loop only?break (no label)
3Skip current iteration?continue
4Time for nested n×n loop?O(n²)
5Stars in pyramid row i?2i+1
6Total stars in triangle?n(n+1)/2
7How to exit outer loop from inner?Labeled break (JS) or return
8for...of vs for...in in JS?of iterates values, in iterates keys
9Range-based for in C++?for (auto x : container)
10Prevent infinite loop?Ensure condition eventually becomes false

Rapid self-check cards

RC-001

  • Q: What are three types of loops?
  • A: for, while, do-while

RC-002

  • Q: When is do-while better than while?
  • A: When the body must execute at least once (menus, validation)

RC-003

  • Q: How does break work in nested loops?
  • A: Exits only the innermost loop

RC-004

  • Q: What is the time complexity of printing a pyramid?
  • A: O(n²) — two nested loops

RC-005

  • Q: How many stars in row i of a pyramid (0-indexed)?
  • A: 2*i + 1 stars

RC-006

  • Q: What causes an infinite loop?
  • A: Loop variable never reaches exit condition

RC-007

  • Q: How do you skip an iteration?
  • A: Use the continue statement

RC-008

  • Q: What is a labeled break?
  • A: A label lets break/continue target an outer loop

RC-009

  • Q: How to iterate backwards?
  • A: for (let i = n-1; i >= 0; i--)

RC-010

  • Q: What is Floyd's triangle?
  • A: Consecutive numbers filling rows: 1 / 2 3 / 4 5 6 / ...

RC-011

  • Q: How to optimize nested loops?
  • A: Use hash maps, sorting, prefix sums, or early termination

RC-012

  • Q: What is the difference between for...of and for...in?
  • A: for...of iterates values, for...in iterates enumerable property names

RC-013

  • Q: How does continue work inside a for loop?
  • A: Jumps to the update expression (i++), then checks the condition

RC-014

  • Q: What is the safeguard against infinite loops?
  • A: Maximum iteration counter with a throw/break if exceeded

RC-015

  • Q: How to print a diamond pattern?
  • A: Pyramid (n rows) + inverted pyramid (n-1 rows)

RC-016

  • Q: What is the total iterations for a triangular pattern?
  • A: n(n+1)/2 — triangular number

RC-017

  • Q: How to exit two nested loops at once?
  • A: Labeled break in JS, or use return from a function

RC-018

  • Q: What is range-based for in C++?
  • A: for (auto x : container) — iterates over elements directly

RC-019

  • Q: How does forEach differ from for...of?
  • A: forEach is a method with callback, for...of is a language statement that supports break

RC-020

  • Q: When should you cache the loop bound?
  • A: When the bound computation is expensive (arr.length is cheap, computed values are not)

RC-021

  • Q: What are three types of loops?
  • A: for, while, do-while

RC-022

  • Q: When is do-while better than while?
  • A: When the body must execute at least once (menus, validation)

RC-023

  • Q: How does break work in nested loops?
  • A: Exits only the innermost loop

RC-024

  • Q: What is the time complexity of printing a pyramid?
  • A: O(n²) — two nested loops

RC-025

  • Q: How many stars in row i of a pyramid (0-indexed)?
  • A: 2*i + 1 stars

RC-026

  • Q: What causes an infinite loop?
  • A: Loop variable never reaches exit condition

RC-027

  • Q: How do you skip an iteration?
  • A: Use the continue statement

RC-028

  • Q: What is a labeled break?
  • A: A label lets break/continue target an outer loop

RC-029

  • Q: How to iterate backwards?
  • A: for (let i = n-1; i >= 0; i--)

RC-030

  • Q: What is Floyd's triangle?
  • A: Consecutive numbers filling rows: 1 / 2 3 / 4 5 6 / ...

RC-031

  • Q: How to optimize nested loops?
  • A: Use hash maps, sorting, prefix sums, or early termination

RC-032

  • Q: What is the difference between for...of and for...in?
  • A: for...of iterates values, for...in iterates enumerable property names

RC-033

  • Q: How does continue work inside a for loop?
  • A: Jumps to the update expression (i++), then checks the condition

RC-034

  • Q: What is the safeguard against infinite loops?
  • A: Maximum iteration counter with a throw/break if exceeded

RC-035

  • Q: How to print a diamond pattern?
  • A: Pyramid (n rows) + inverted pyramid (n-1 rows)

RC-036

  • Q: What is the total iterations for a triangular pattern?
  • A: n(n+1)/2 — triangular number

RC-037

  • Q: How to exit two nested loops at once?
  • A: Labeled break in JS, or use return from a function

RC-038

  • Q: What is range-based for in C++?
  • A: for (auto x : container) — iterates over elements directly

RC-039

  • Q: How does forEach differ from for...of?
  • A: forEach is a method with callback, for...of is a language statement that supports break

RC-040

  • Q: When should you cache the loop bound?
  • A: When the bound computation is expensive (arr.length is cheap, computed values are not)

RC-041

  • Q: What are three types of loops?
  • A: for, while, do-while

RC-042

  • Q: When is do-while better than while?
  • A: When the body must execute at least once (menus, validation)

RC-043

  • Q: How does break work in nested loops?
  • A: Exits only the innermost loop

RC-044

  • Q: What is the time complexity of printing a pyramid?
  • A: O(n²) — two nested loops

RC-045

  • Q: How many stars in row i of a pyramid (0-indexed)?
  • A: 2*i + 1 stars

RC-046

  • Q: What causes an infinite loop?
  • A: Loop variable never reaches exit condition

RC-047

  • Q: How do you skip an iteration?
  • A: Use the continue statement

RC-048

  • Q: What is a labeled break?
  • A: A label lets break/continue target an outer loop

RC-049

  • Q: How to iterate backwards?
  • A: for (let i = n-1; i >= 0; i--)

RC-050

  • Q: What is Floyd's triangle?
  • A: Consecutive numbers filling rows: 1 / 2 3 / 4 5 6 / ...

RC-051

  • Q: How to optimize nested loops?
  • A: Use hash maps, sorting, prefix sums, or early termination

RC-052

  • Q: What is the difference between for...of and for...in?
  • A: for...of iterates values, for...in iterates enumerable property names

RC-053

  • Q: How does continue work inside a for loop?
  • A: Jumps to the update expression (i++), then checks the condition

RC-054

  • Q: What is the safeguard against infinite loops?
  • A: Maximum iteration counter with a throw/break if exceeded

RC-055

  • Q: How to print a diamond pattern?
  • A: Pyramid (n rows) + inverted pyramid (n-1 rows)

RC-056

  • Q: What is the total iterations for a triangular pattern?
  • A: n(n+1)/2 — triangular number

RC-057

  • Q: How to exit two nested loops at once?
  • A: Labeled break in JS, or use return from a function

RC-058

  • Q: What is range-based for in C++?
  • A: for (auto x : container) — iterates over elements directly

RC-059

  • Q: How does forEach differ from for...of?
  • A: forEach is a method with callback, for...of is a language statement that supports break

RC-060

  • Q: When should you cache the loop bound?
  • A: When the bound computation is expensive (arr.length is cheap, computed values are not)

RC-061

  • Q: What are three types of loops?
  • A: for, while, do-while

RC-062

  • Q: When is do-while better than while?
  • A: When the body must execute at least once (menus, validation)

RC-063

  • Q: How does break work in nested loops?
  • A: Exits only the innermost loop

RC-064

  • Q: What is the time complexity of printing a pyramid?
  • A: O(n²) — two nested loops

RC-065

  • Q: How many stars in row i of a pyramid (0-indexed)?
  • A: 2*i + 1 stars

RC-066

  • Q: What causes an infinite loop?
  • A: Loop variable never reaches exit condition

RC-067

  • Q: How do you skip an iteration?
  • A: Use the continue statement

RC-068

  • Q: What is a labeled break?
  • A: A label lets break/continue target an outer loop

RC-069

  • Q: How to iterate backwards?
  • A: for (let i = n-1; i >= 0; i--)

RC-070

  • Q: What is Floyd's triangle?
  • A: Consecutive numbers filling rows: 1 / 2 3 / 4 5 6 / ...

RC-071

  • Q: How to optimize nested loops?
  • A: Use hash maps, sorting, prefix sums, or early termination

RC-072

  • Q: What is the difference between for...of and for...in?
  • A: for...of iterates values, for...in iterates enumerable property names

RC-073

  • Q: How does continue work inside a for loop?
  • A: Jumps to the update expression (i++), then checks the condition

RC-074

  • Q: What is the safeguard against infinite loops?
  • A: Maximum iteration counter with a throw/break if exceeded

RC-075

  • Q: How to print a diamond pattern?
  • A: Pyramid (n rows) + inverted pyramid (n-1 rows)

RC-076

  • Q: What is the total iterations for a triangular pattern?
  • A: n(n+1)/2 — triangular number

RC-077

  • Q: How to exit two nested loops at once?
  • A: Labeled break in JS, or use return from a function

RC-078

  • Q: What is range-based for in C++?
  • A: for (auto x : container) — iterates over elements directly

RC-079

  • Q: How does forEach differ from for...of?
  • A: forEach is a method with callback, for...of is a language statement that supports break

RC-080

  • Q: When should you cache the loop bound?
  • A: When the bound computation is expensive (arr.length is cheap, computed values are not)

RC-081

  • Q: What are three types of loops?
  • A: for, while, do-while

RC-082

  • Q: When is do-while better than while?
  • A: When the body must execute at least once (menus, validation)

RC-083

  • Q: How does break work in nested loops?
  • A: Exits only the innermost loop

RC-084

  • Q: What is the time complexity of printing a pyramid?
  • A: O(n²) — two nested loops

RC-085

  • Q: How many stars in row i of a pyramid (0-indexed)?
  • A: 2*i + 1 stars

RC-086

  • Q: What causes an infinite loop?
  • A: Loop variable never reaches exit condition

RC-087

  • Q: How do you skip an iteration?
  • A: Use the continue statement

RC-088

  • Q: What is a labeled break?
  • A: A label lets break/continue target an outer loop

RC-089

  • Q: How to iterate backwards?
  • A: for (let i = n-1; i >= 0; i--)

RC-090

  • Q: What is Floyd's triangle?
  • A: Consecutive numbers filling rows: 1 / 2 3 / 4 5 6 / ...

RC-091

  • Q: How to optimize nested loops?
  • A: Use hash maps, sorting, prefix sums, or early termination

RC-092

  • Q: What is the difference between for...of and for...in?
  • A: for...of iterates values, for...in iterates enumerable property names

RC-093

  • Q: How does continue work inside a for loop?
  • A: Jumps to the update expression (i++), then checks the condition

RC-094

  • Q: What is the safeguard against infinite loops?
  • A: Maximum iteration counter with a throw/break if exceeded

RC-095

  • Q: How to print a diamond pattern?
  • A: Pyramid (n rows) + inverted pyramid (n-1 rows)

RC-096

  • Q: What is the total iterations for a triangular pattern?
  • A: n(n+1)/2 — triangular number

RC-097

  • Q: How to exit two nested loops at once?
  • A: Labeled break in JS, or use return from a function

RC-098

  • Q: What is range-based for in C++?
  • A: for (auto x : container) — iterates over elements directly

RC-099

  • Q: How does forEach differ from for...of?
  • A: forEach is a method with callback, for...of is a language statement that supports break

RC-100

  • Q: When should you cache the loop bound?
  • A: When the bound computation is expensive (arr.length is cheap, computed values are not)

RC-101

  • Q: What are three types of loops?
  • A: for, while, do-while

RC-102

  • Q: When is do-while better than while?
  • A: When the body must execute at least once (menus, validation)

RC-103

  • Q: How does break work in nested loops?
  • A: Exits only the innermost loop

RC-104

  • Q: What is the time complexity of printing a pyramid?
  • A: O(n²) — two nested loops

RC-105

  • Q: How many stars in row i of a pyramid (0-indexed)?
  • A: 2*i + 1 stars

RC-106

  • Q: What causes an infinite loop?
  • A: Loop variable never reaches exit condition

RC-107

  • Q: How do you skip an iteration?
  • A: Use the continue statement

RC-108

  • Q: What is a labeled break?
  • A: A label lets break/continue target an outer loop

RC-109

  • Q: How to iterate backwards?
  • A: for (let i = n-1; i >= 0; i--)

RC-110

  • Q: What is Floyd's triangle?
  • A: Consecutive numbers filling rows: 1 / 2 3 / 4 5 6 / ...

RC-111

  • Q: How to optimize nested loops?
  • A: Use hash maps, sorting, prefix sums, or early termination

RC-112

  • Q: What is the difference between for...of and for...in?
  • A: for...of iterates values, for...in iterates enumerable property names

RC-113

  • Q: How does continue work inside a for loop?
  • A: Jumps to the update expression (i++), then checks the condition

RC-114

  • Q: What is the safeguard against infinite loops?
  • A: Maximum iteration counter with a throw/break if exceeded

RC-115

  • Q: How to print a diamond pattern?
  • A: Pyramid (n rows) + inverted pyramid (n-1 rows)

RC-116

  • Q: What is the total iterations for a triangular pattern?
  • A: n(n+1)/2 — triangular number

RC-117

  • Q: How to exit two nested loops at once?
  • A: Labeled break in JS, or use return from a function

RC-118

  • Q: What is range-based for in C++?
  • A: for (auto x : container) — iterates over elements directly

RC-119

  • Q: How does forEach differ from for...of?
  • A: forEach is a method with callback, for...of is a language statement that supports break

RC-120

  • Q: When should you cache the loop bound?
  • A: When the bound computation is expensive (arr.length is cheap, computed values are not)

RC-121

  • Q: What are three types of loops?
  • A: for, while, do-while

RC-122

  • Q: When is do-while better than while?
  • A: When the body must execute at least once (menus, validation)

RC-123

  • Q: How does break work in nested loops?
  • A: Exits only the innermost loop

RC-124

  • Q: What is the time complexity of printing a pyramid?
  • A: O(n²) — two nested loops

RC-125

  • Q: How many stars in row i of a pyramid (0-indexed)?
  • A: 2*i + 1 stars

RC-126

  • Q: What causes an infinite loop?
  • A: Loop variable never reaches exit condition

RC-127

  • Q: How do you skip an iteration?
  • A: Use the continue statement

RC-128

  • Q: What is a labeled break?
  • A: A label lets break/continue target an outer loop

RC-129

  • Q: How to iterate backwards?
  • A: for (let i = n-1; i >= 0; i--)

RC-130

  • Q: What is Floyd's triangle?
  • A: Consecutive numbers filling rows: 1 / 2 3 / 4 5 6 / ...

RC-131

  • Q: How to optimize nested loops?
  • A: Use hash maps, sorting, prefix sums, or early termination

RC-132

  • Q: What is the difference between for...of and for...in?
  • A: for...of iterates values, for...in iterates enumerable property names

RC-133

  • Q: How does continue work inside a for loop?
  • A: Jumps to the update expression (i++), then checks the condition

RC-134

  • Q: What is the safeguard against infinite loops?
  • A: Maximum iteration counter with a throw/break if exceeded

RC-135

  • Q: How to print a diamond pattern?
  • A: Pyramid (n rows) + inverted pyramid (n-1 rows)

RC-136

  • Q: What is the total iterations for a triangular pattern?
  • A: n(n+1)/2 — triangular number

RC-137

  • Q: How to exit two nested loops at once?
  • A: Labeled break in JS, or use return from a function

RC-138

  • Q: What is range-based for in C++?
  • A: for (auto x : container) — iterates over elements directly

RC-139

  • Q: How does forEach differ from for...of?
  • A: forEach is a method with callback, for...of is a language statement that supports break

RC-140

  • Q: When should you cache the loop bound?
  • A: When the bound computation is expensive (arr.length is cheap, computed values are not)

RC-141

  • Q: What are three types of loops?
  • A: for, while, do-while

RC-142

  • Q: When is do-while better than while?
  • A: When the body must execute at least once (menus, validation)

RC-143

  • Q: How does break work in nested loops?
  • A: Exits only the innermost loop

RC-144

  • Q: What is the time complexity of printing a pyramid?
  • A: O(n²) — two nested loops

RC-145

  • Q: How many stars in row i of a pyramid (0-indexed)?
  • A: 2*i + 1 stars

RC-146

  • Q: What causes an infinite loop?
  • A: Loop variable never reaches exit condition

RC-147

  • Q: How do you skip an iteration?
  • A: Use the continue statement

RC-148

  • Q: What is a labeled break?
  • A: A label lets break/continue target an outer loop

RC-149

  • Q: How to iterate backwards?
  • A: for (let i = n-1; i >= 0; i--)

RC-150

  • Q: What is Floyd's triangle?
  • A: Consecutive numbers filling rows: 1 / 2 3 / 4 5 6 / ...

RC-151

  • Q: How to optimize nested loops?
  • A: Use hash maps, sorting, prefix sums, or early termination

RC-152

  • Q: What is the difference between for...of and for...in?
  • A: for...of iterates values, for...in iterates enumerable property names

RC-153

  • Q: How does continue work inside a for loop?
  • A: Jumps to the update expression (i++), then checks the condition

RC-154

  • Q: What is the safeguard against infinite loops?
  • A: Maximum iteration counter with a throw/break if exceeded

RC-155

  • Q: How to print a diamond pattern?
  • A: Pyramid (n rows) + inverted pyramid (n-1 rows)

RC-156

  • Q: What is the total iterations for a triangular pattern?
  • A: n(n+1)/2 — triangular number

RC-157

  • Q: How to exit two nested loops at once?
  • A: Labeled break in JS, or use return from a function

RC-158

  • Q: What is range-based for in C++?
  • A: for (auto x : container) — iterates over elements directly

RC-159

  • Q: How does forEach differ from for...of?
  • A: forEach is a method with callback, for...of is a language statement that supports break

RC-160

  • Q: When should you cache the loop bound?
  • A: When the bound computation is expensive (arr.length is cheap, computed values are not)

RC-161

  • Q: What are three types of loops?
  • A: for, while, do-while

RC-162

  • Q: When is do-while better than while?
  • A: When the body must execute at least once (menus, validation)

RC-163

  • Q: How does break work in nested loops?
  • A: Exits only the innermost loop

RC-164

  • Q: What is the time complexity of printing a pyramid?
  • A: O(n²) — two nested loops

RC-165

  • Q: How many stars in row i of a pyramid (0-indexed)?
  • A: 2*i + 1 stars

RC-166

  • Q: What causes an infinite loop?
  • A: Loop variable never reaches exit condition

RC-167

  • Q: How do you skip an iteration?
  • A: Use the continue statement

RC-168

  • Q: What is a labeled break?
  • A: A label lets break/continue target an outer loop

RC-169

  • Q: How to iterate backwards?
  • A: for (let i = n-1; i >= 0; i--)

RC-170

  • Q: What is Floyd's triangle?
  • A: Consecutive numbers filling rows: 1 / 2 3 / 4 5 6 / ...

RC-171

  • Q: How to optimize nested loops?
  • A: Use hash maps, sorting, prefix sums, or early termination

RC-172

  • Q: What is the difference between for...of and for...in?
  • A: for...of iterates values, for...in iterates enumerable property names

RC-173

  • Q: How does continue work inside a for loop?
  • A: Jumps to the update expression (i++), then checks the condition

RC-174

  • Q: What is the safeguard against infinite loops?
  • A: Maximum iteration counter with a throw/break if exceeded

RC-175

  • Q: How to print a diamond pattern?
  • A: Pyramid (n rows) + inverted pyramid (n-1 rows)

RC-176

  • Q: What is the total iterations for a triangular pattern?
  • A: n(n+1)/2 — triangular number

RC-177

  • Q: How to exit two nested loops at once?
  • A: Labeled break in JS, or use return from a function

RC-178

  • Q: What is range-based for in C++?
  • A: for (auto x : container) — iterates over elements directly

RC-179

  • Q: How does forEach differ from for...of?
  • A: forEach is a method with callback, for...of is a language statement that supports break

RC-180

  • Q: When should you cache the loop bound?
  • A: When the bound computation is expensive (arr.length is cheap, computed values are not)

RC-181

  • Q: What are three types of loops?
  • A: for, while, do-while

RC-182

  • Q: When is do-while better than while?
  • A: When the body must execute at least once (menus, validation)

RC-183

  • Q: How does break work in nested loops?
  • A: Exits only the innermost loop

RC-184

  • Q: What is the time complexity of printing a pyramid?
  • A: O(n²) — two nested loops

RC-185

  • Q: How many stars in row i of a pyramid (0-indexed)?
  • A: 2*i + 1 stars

RC-186

  • Q: What causes an infinite loop?
  • A: Loop variable never reaches exit condition

RC-187

  • Q: How do you skip an iteration?
  • A: Use the continue statement

RC-188

  • Q: What is a labeled break?
  • A: A label lets break/continue target an outer loop

RC-189

  • Q: How to iterate backwards?
  • A: for (let i = n-1; i >= 0; i--)

RC-190

  • Q: What is Floyd's triangle?
  • A: Consecutive numbers filling rows: 1 / 2 3 / 4 5 6 / ...

RC-191

  • Q: How to optimize nested loops?
  • A: Use hash maps, sorting, prefix sums, or early termination

RC-192

  • Q: What is the difference between for...of and for...in?
  • A: for...of iterates values, for...in iterates enumerable property names

RC-193

  • Q: How does continue work inside a for loop?
  • A: Jumps to the update expression (i++), then checks the condition

RC-194

  • Q: What is the safeguard against infinite loops?
  • A: Maximum iteration counter with a throw/break if exceeded

RC-195

  • Q: How to print a diamond pattern?
  • A: Pyramid (n rows) + inverted pyramid (n-1 rows)

RC-196

  • Q: What is the total iterations for a triangular pattern?
  • A: n(n+1)/2 — triangular number

RC-197

  • Q: How to exit two nested loops at once?
  • A: Labeled break in JS, or use return from a function

RC-198

  • Q: What is range-based for in C++?
  • A: for (auto x : container) — iterates over elements directly

RC-199

  • Q: How does forEach differ from for...of?
  • A: forEach is a method with callback, for...of is a language statement that supports break

RC-200

  • Q: When should you cache the loop bound?
  • A: When the bound computation is expensive (arr.length is cheap, computed values are not)