{"id":2704,"date":"2026-02-05T10:55:04","date_gmt":"2026-02-05T10:55:04","guid":{"rendered":"https:\/\/demo.materiamedica.net\/demo6\/?p=2704"},"modified":"2026-02-05T10:55:04","modified_gmt":"2026-02-05T10:55:04","slug":"chapter-59-swift-nested-loops","status":"publish","type":"post","link":"https:\/\/demo.materiamedica.net\/demo6\/chapter-59-swift-nested-loops\/","title":{"rendered":"Chapter 59: Swift Nested Loops"},"content":{"rendered":"1. What is a nested loop? (very clear definition)<\/h3>\n
A nested loop<\/strong> means one loop inside another loop<\/strong>.<\/p>\nThe inner loop runs completely<\/strong> for every single iteration<\/strong> of the outer loop.<\/p>\nAnalogy that almost everyone understands:<\/p>\n
Think of a calendar<\/strong>:<\/p>\n\n- Outer loop = months<\/strong> (12 times)<\/li>\n
- Inner loop = days<\/strong> in that month (28\u201331 times)<\/li>\n<\/ul>\n
For each month, you go through every day \u2192 total iterations = sum of days in each month.<\/p>\n
In code terms:<\/p>\n
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for outer in something { \/\/ runs 5 times\r\n for inner in somethingElse { \/\/ runs 3 times for EACH outer iteration\r\n print(\"outer:\\(outer), inner:\\(inner)\")\r\n }\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nTotal prints: 5 \u00d7 3 = 15 times<\/p>\n
2. The classic first example \u2013 multiplication table<\/h3>\n\n
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print(\"Multiplication Table (1 to 10)\")\r\nprint(\"-----------------------------\")\r\n\r\nfor row in 1...10 {\r\n var line = \"\"\r\n \r\n for column in 1...10 {\r\n let product = row * column\r\n line += String(format: \"%4d\", product) + \" \"\r\n }\r\n \r\n print(line)\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nOutput (partial):<\/p>\n
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text<\/div>\n
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Multiplication Table (1 to 10)\r\n-----------------------------\r\n 1 2 3 4 5 6 7 8 9 10 \r\n 2 4 6 8 10 12 14 16 18 20 \r\n 3 6 9 12 15 18 21 24 27 30 \r\n...<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nWhy nested loops are natural here:<\/strong><\/p>\n\n- Outer loop = rows (which number we are multiplying)<\/li>\n
- Inner loop = columns (1 \u00d7 row, 2 \u00d7 row, 3 \u00d7 row, \u2026)<\/li>\n<\/ul>\n
3. Real-life example 1 \u2013 Tic-tac-toe board (2D grid)<\/h3>\n\n
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var board = [\r\n [\" \", \" \", \" \"],\r\n [\" \", \" \", \" \"],\r\n [\" \", \" \", \" \"]\r\n]\r\n\r\n\/\/ Place some moves\r\nboard[0][0] = \"X\"\r\nboard[1][1] = \"O\"\r\nboard[2][2] = \"X\"\r\n\r\n\/\/ Print the board nicely\r\nprint(\" 0 1 2\")\r\nprint(\" -------\")\r\n\r\nfor rowIndex in 0..<board.count {\r\n print(\"\\(rowIndex)|\", terminator: \"\")\r\n \r\n for colIndex in 0..<board[rowIndex].count {\r\n let cell = board[rowIndex][colIndex]\r\n print(\" \\(cell) \", terminator: \"\")\r\n \r\n if colIndex < board[rowIndex].count - 1 {\r\n print(\"|\", terminator: \"\")\r\n }\r\n }\r\n \r\n print()\r\n \r\n if rowIndex < board.count - 1 {\r\n print(\" -------\")\r\n }\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nOutput:<\/p>\n
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0 1 2\r\n -------\r\n0| X | | \r\n -------\r\n1| | O | \r\n -------\r\n2| | | X<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nKey learning points:<\/strong><\/p>\n\n- Outer loop = rows<\/li>\n
- Inner loop = columns inside each row<\/li>\n
- We use two indices: rowIndex and colIndex<\/li>\n<\/ul>\n
4. Real-life example 2 \u2013 Seating arrangement \/ table plan<\/h3>\n\n
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let tables = [\r\n [\"Rahul\", \"Priya\", \"Aarav\"],\r\n [\"Sneha\", \"Karan\", \"Meera\", \"Vikram\"],\r\n [\"Ananya\", \"Rohan\"]\r\n]\r\n\r\nprint(\"Wedding Table Seating\")\r\nprint(\"=====================\")\r\n\r\nfor tableNumber in 0..<tables.count {\r\n print(\"Table \\(tableNumber + 1):\")\r\n \r\n for (seat, guest) in tables[tableNumber].enumerated() {\r\n print(\" Seat \\(seat + 1): \\(guest)\")\r\n }\r\n \r\n print()\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nOutput:<\/p>\n
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text<\/div>\n
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Wedding Table Seating\r\n=====================\r\nTable 1:\r\n Seat 1: Rahul\r\n Seat 2: Priya\r\n Seat 3: Aarav\r\n\r\nTable 2:\r\n Seat 1: Sneha\r\n Seat 2: Karan\r\n Seat 3: Meera\r\n Seat 4: Vikram\r\n\r\nTable 3:\r\n Seat 1: Ananya\r\n Seat 2: Rohan<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nTypical pattern<\/strong>:<\/p>\n\n- Outer loop = tables \/ groups \/ categories<\/li>\n
- Inner loop = people \/ items \/ sub-items inside each group<\/li>\n<\/ul>\n
5. Real-life example 3 \u2013 Search \/ filter in 2D data<\/h3>\n\n
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Swift<\/div>\n
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let students = [\r\n [\"Rahul\", \"A\", 92],\r\n [\"Priya\", \"A\", 98],\r\n [\"Aarav\", \"B\", 85],\r\n [\"Sneha\", \"A+\", 95],\r\n [\"Karan\", \"C\", 68]\r\n]\r\n\r\nprint(\"Students who scored 90+:\")\r\n\r\nfor student in students {\r\n let name = student[0] as! String\r\n let grade = student[1] as! String\r\n let marks = student[2] as! Int\r\n \r\n if marks >= 90 {\r\n print(\" \u2022 \\(name) \u2013 \\(grade) (\\(marks)%)\")\r\n }\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nOutput:<\/p>\n
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text<\/div>\n
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Students who scored 90+:\r\n \u2022 Priya \u2013 A (98%)\r\n \u2022 Sneha \u2013 A+ (95%)<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n6. Real-life example 4 \u2013 Pattern printing (great for understanding nesting)<\/h3>\n\n
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Swift<\/div>\n
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let size = 5\r\n\r\nfor row in 1...size {\r\n for _ in 1...row {\r\n print(\"*\", terminator: \"\")\r\n }\r\n print()\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nOutput:<\/p>\n
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*\r\n**\r\n***\r\n****\r\n*****<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nReverse pattern<\/strong>:<\/p>\n\n
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Swift<\/div>\n
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for row in 1...size {\r\n \/\/ spaces first\r\n for _ in 1...(size - row) {\r\n print(\" \", terminator: \"\")\r\n }\r\n \r\n \/\/ stars\r\n for _ in 1...row {\r\n print(\"*\", terminator: \"\")\r\n }\r\n \r\n print()\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nOutput:<\/p>\n
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*\r\n **\r\n ***\r\n ****\r\n*****<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n7. Very Common Beginner Mistakes & How to Avoid Them<\/h3>\n\n
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\n\n\n| Mistake<\/th>\n | Wrong \/ Dangerous code<\/th>\n | Correct \/ Better habit<\/th>\n | Why?<\/th>\n<\/tr>\n<\/thead>\n |
\n\n| Modifying outer collection inside inner loop<\/td>\n | for row in grid { for cell in row { grid.append(\u2026) } }<\/td>\n | Build new collection or use indices<\/td>\n | Collection mutated while being iterated \u2013 crash<\/td>\n<\/tr>\n |
\n| Forgetting to reset inner counter<\/td>\n | for i in 1…5 { for j in 1…5 { print(i,j) } } (but j not reset)<\/td>\n | Each inner loop is independent<\/td>\n | Inner loop resets automatically<\/td>\n<\/tr>\n |
\n| Using wrong index range<\/td>\n | for i in 0…rows { \u2026 }<\/td>\n | for i in 0..<rows { \u2026 }<\/td>\n | 0…rows.count tries to access out-of-bounds<\/td>\n<\/tr>\n |
\n| Deep nesting (pyramid of doom)<\/td>\n | 5+ levels of nested for\/if<\/td>\n | Extract to functions or flatten logic<\/td>\n | Code becomes unreadable & hard to debug<\/td>\n<\/tr>\n |
\n| Assuming all rows have same length<\/td>\n | matrix[row][col] without check<\/td>\n | if col < matrix[row].count { \u2026 }<\/td>\n | Rows can have different lengths<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n 8. Quick Reference \u2013 Most Used Nested Loop Patterns<\/h3>\n\n \n \n\n\n| Goal<\/th>\n | Typical nested loop structure<\/th>\n | Real-life feeling \/ use-case<\/th>\n<\/tr>\n<\/thead>\n | \n\n| Print 2D grid \/ table<\/td>\n | for row in rows { for col in columns { \u2026 } }<\/td>\n | Chessboard, calendar, spreadsheet view<\/td>\n<\/tr>\n | \n| Process rows & columns independently<\/td>\n | for row in matrix { for cell in row { \u2026 } }<\/td>\n | Matrix math, image processing, game board<\/td>\n<\/tr>\n | \n| Numbered list inside groups<\/td>\n | for group in groups { for (i, item) in group.enumerated() { \u2026 } }<\/td>\n | Seating plan, grouped tasks, multi-team leaderboard<\/td>\n<\/tr>\n | \n| Pattern printing (stars, numbers, shapes)<\/td>\n | for row in 1…n { for col in 1…row { print(“*”) } }<\/td>\n | Understanding loops, interview questions<\/td>\n<\/tr>\n | \n| Search \/ filter in 2D data<\/td>\n | for row in data { for item in row { if condition { \u2026 } } }<\/td>\n | Find all matching cells, count occurrences<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n 9. Small Practice \u2013 Try these<\/h3>\n\n- Mini multiplication table<\/strong> (5\u00d75) Print 1\u00d71 to 5\u00d75 using nested for<\/li>\n
- Right-aligned triangle of stars<\/strong> For size = 5, print:<\/li>\n<\/ol>\n
\n \n \n text<\/div>\n \n *\r\n **\r\n ***\r\n ****\r\n*****<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n\n- Print a 4\u00d76 grid of coordinates<\/strong> Output should look like:<\/li>\n<\/ol>\n
\n \n \n text<\/div>\n \n (0,0) (0,1) (0,2) (0,3) (0,4) (0,5)\r\n(1,0) (1,1) (1,2) (1,3) (1,4) (1,5)\r\n(2,0) (2,1) (2,2) (2,3) (2,4) (2,5)\r\n(3,0) (3,1) (3,2) (3,3) (3,4) (3,5)<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nPaste your code here if you want feedback or want to see cleaner \/ more elegant versions!<\/p>\n What would you like to explore next?<\/p>\n \n- Nested loops with break<\/strong> and continue<\/strong><\/li>\n
- Nested loops in SwiftUI<\/strong> (ForEach inside ForEach)<\/li>\n
- How to flatten<\/strong> nested loops into functional style (flatMap, map + joined)<\/li>\n
- Multidimensional arrays + nested loops (2D tables, grids\u2026)<\/li>\n
- Or move to another topic (dictionaries, sets, optionals, switch\u2026)<\/li>\n<\/ul>\n
Just tell me \u2014 we\u2019ll continue in the same clear, patient, detailed style \ud83d\ude0a<\/p>\n","protected":false},"excerpt":{"rendered":" 1. What is a nested loop? (very clear definition) A nested loop means one loop inside another loop. The inner loop runs completely for every single iteration of the outer loop. Analogy that almost...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[76],"tags":[],"class_list":["post-2704","post","type-post","status-publish","format-standard","hentry","category-swift"],"_links":{"self":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2704","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/comments?post=2704"}],"version-history":[{"count":1,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2704\/revisions"}],"predecessor-version":[{"id":2705,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2704\/revisions\/2705"}],"wp:attachment":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/media?parent=2704"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/categories?post=2704"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/tags?post=2704"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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