7.2 — Quick Revision: Loops, Nested Loops & Patterns

<< Overview

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Loop types cheat sheet

for (init; cond; update) { body }   ← known count
while (cond) { body }               ← unknown count
do { body } while (cond);           ← at least once

Key formulas for patterns

Pattern	Spaces per row	Stars/chars per row
Right triangle	0	i
Inverted triangle	0	n - i
Centered pyramid	n-1-i	2i+1
Diamond (upper)	n-1-i	2i+1
Diamond (lower)	n-1-i (counting down)	2i+1

break vs continue

Statement	Effect
break	Exit innermost loop
continue	Skip to next iteration
labeled break	Exit named loop

Complexity

Loop pattern	Complexity
Single loop	O(n)
Nested (n×n)	O(n²)
Loop to √n	O(√n)
Halving loop	O(log n)
Triple nested	O(n³)

Infinite loop prevention

1. Always update the loop variable
2. Ensure condition will eventually be false
3. Use a max iteration safeguard
4. Avoid floating-point exact comparisons

Common pitfalls

1. Off-by-one errors (< vs <=)
2. Forgetting to increment counter
3. Wrong loop variable in nested loops (i vs j)
4. Modifying array while iterating
5. Using = instead of === in condition

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Self-check drill

SC-001

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-002

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-003

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-004

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-005

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-006

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

SC-007

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

SC-008

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-009

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-010

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-011

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-012

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-013

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-014

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-015

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-016

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

SC-017

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

SC-018

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-019

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-020

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-021

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-022

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-023

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-024

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-025

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-026

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

SC-027

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

SC-028

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-029

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-030

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-031

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-032

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-033

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-034

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-035

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-036

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

SC-037

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

SC-038

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-039

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-040

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-041

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-042

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-043

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-044

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-045

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-046

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

SC-047

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

SC-048

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-049

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-050

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-051

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-052

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-053

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-054

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-055

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-056

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

SC-057

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

SC-058

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-059

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-060

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-061

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-062

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-063

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-064

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-065

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-066

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

SC-067

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

SC-068

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-069

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-070

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-071

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-072

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-073

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-074

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-075

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-076

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

SC-077

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

SC-078

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-079

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-080

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-081

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-082

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-083

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-084

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-085

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-086

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

SC-087

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

SC-088

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-089

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-090

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-091

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-092

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-093

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-094

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-095

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-096

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

SC-097

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

SC-098

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-099

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-100

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-101

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-102

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-103

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-104

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-105

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-106

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

SC-107

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

SC-108

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-109

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-110

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-111

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-112

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-113

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-114

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-115

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-116

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

SC-117

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

SC-118

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-119

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-120

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-121

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-122

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-123

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-124

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-125

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-126

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

SC-127

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

SC-128

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-129

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-130

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-131

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-132

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-133

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-134

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-135

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-136

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

SC-137

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

SC-138

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-139

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-140

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-141

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-142

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-143

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-144

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-145

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-146

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

SC-147

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

SC-148

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-149

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-150

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-151

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-152

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-153

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-154

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-155

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-156

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

SC-157

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

SC-158

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-159

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-160

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-161

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-162

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-163

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-164

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-165

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-166

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

SC-167

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

SC-168

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-169

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-170

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-171

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-172

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-173

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-174

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-175

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-176

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

SC-177

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

SC-178

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-179

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-180

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-181

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-182

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-183

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-184

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-185

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-186

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

SC-187

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

SC-188

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-189

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-190

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function

SC-191

• Q: What are the three parts of a for loop?
• A: initialization; condition; update

SC-192

• Q: When does a do-while body execute?
• A: At least once, before the condition is checked

SC-193

• Q: What does break do?
• A: Exits the innermost enclosing loop

SC-194

• Q: What does continue do?
• A: Skips the rest of the current iteration

SC-195

• Q: Time complexity of nested n×n loop?
• A: O(n²)

SC-196

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

SC-197

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

SC-198

• Q: How to prevent infinite loops?
• A: Ensure loop variable changes and condition becomes false

SC-199

• Q: Difference between for...of and for...in?
• A: for...of: values; for...in: enumerable property names/keys

SC-200

• Q: How to exit outer loop from inner?
• A: Labeled break (JS) or return from function