Category: 01. Basic

Swift Nested Loops

Place a loop inside another loop to generate combinations or matrices.

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Generate combinations with nested loops

Use inner and outer loops to produce pairs or grids from ranges and collections.

Example

for i in 1...2 {
  for j in 1...3 {
print(i, j)
  }
}

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Multiplication Table

Use nested loops to build a small multiplication table.

Example

for i in 1...3 {
  var row = ""
  for j in 1...3 {
row += "\(i*j) "
  }
  print(row)
}

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Swift For Loop

Use for-in to iterate over ranges, arrays, dictionaries, and other sequences.

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Iterate a Range

Use a range to loop a fixed number of times.

Example

for i in 1...3 {
  print(i)
}

This example iterates from 1 to 3 inclusive.

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Iterate an Array

Loop through an array with for-in or enumerated() to access index and value.

Example

let nums = [10, 20, 30]
for n in nums {
  print(n)
}
for (index, value) in nums.enumerated() {
  print("index: \(index), value: \(value)")
}

Use enumerated() to get index and value together.

Swift While (Real-Life Examples)

Use loops to retry operations, poll statuses, or process queues carefully with exit conditions.

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While Loop from 3 to 1

Count down from 3 to 1.

Example

var remaining = 3
while remaining > 0 {
  print("Remaining: \(remaining)")
  remaining -= 1
}

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Poll Until Success

Repeat an action with a cap on attempts until a condition is met.

Example

var attempts = 0
var success = false
while !success && attempts < 5 {
  attempts += 1
  print("Checking... #\(attempts)")
  if attempts == 3 {
success = true
print("Success!")
  }
}

Swift Repeat/While Loop

Use repeat { ... } while condition to run the body at least once.

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Repeat/while Loop Example

This example uses a repeat/while loop to print “Try #1” and “Try #2”.

Example

var attempts = 0
repeat {
  attempts += 1
  print("Attempt #\(attempts)")
} while attempts < 3

This example demonstrates repeat (do-while style).

Tip: Avoid infinite loops. Ensure the loop condition will eventually become false.

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REMOVE ADS

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Runs Once Even If Condition Is False

Because repeat checks the condition after the body, it executes at least once.

Example

var n = 0
repeat {
  print("Runs once")
} while n > 0

Repeat code while a condition is true using while.

Use repeat { ... } while to check the condition after the loop body.

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while

The while loop checks the condition before each iteration.

Example

var n = 3
while n > 0 {
  print(n)
  n -= 1
}
print("Liftoff!")

This example counts down from 3 using a while loop.

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repeat { } while

repeat runs the body first, then checks the condition.

Example

var attempts = 0
repeat {
  attempts += 1
  print("Attempt #\(attempts)")
} while attempts < 3

This example demonstrates repeat (do-while style).

Swift Switch

Use switch to match a value against patterns.

In Swift, a switch must list every choice, and it stops checking more choices after the first match.

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Basic Switch

Match integer ranges and exact values.

Add default to handle remaining cases.

Example

let grade = 82
switch grade {
case 90...100:
  print("A")
case 80..<90:
  print("B")
case 70..<80:
  print("C")
default:
  print("Below C")
}

This example categorizes a score using ranges in switch.

Note: Swift switch must be exhaustive. Use default to cover remaining cases.

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String Switch

Switch can match strings directly against literal cases.

Example

let command = "start"
switch command {
case "start":
  print("Starting")
case "stop":
  print("Stopping")
default:
  print("Unknown")
}

Swift If (Real-Life Examples)

Apply conditional logic to real situations like validation, feature flags, or permissions.

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Validate input with conditions

Use conditions to validate input and guard against empty or invalid values.

Example

let input = "hello"
if !input.isEmpty {
  print("Input received: \(input)")
}

When the input is empty, the code inside the condition is skipped.

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Feature Flag

Gate a feature behind a flag and a user group.

Example

let enabled = true
let userGroup = "beta"
if enabled && userGroup == "beta" {
  print("Show feature")
}

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Swift If with Logical Operators

Combine conditions with &&, ||, and negate with !.

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Combine conditions with logical operators

Use AND, OR, and NOT to build complex conditions that control code paths.

Example

let isMember = true
let hasCoupon = false
if isMember || hasCoupon {
  print("Discount applied")
}

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AND and NOT

Combine conditions with && and negate with !.

Example

let isMember = true
let expired = false
if isMember && !expired {
  print("Active member")
}

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Swift Nested If

Nest if statements to check multiple levels of conditions.

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Use nested conditions for multi-step checks

Use nested conditions to handle layered checks, such as authentication then role.

Example

let isLoggedIn = true
let isAdmin = false
if isLoggedIn {
if isAdmin {
  print("Admin panel")
} else {
  print("Limited access")
}
  }

Use nested conditions to handle layered checks, such as authentication then role.

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Validate and Branch

Validate inputs first, then use a nested if to branch inside the valid case.

Example

let score = 85
if score >= 0 && score <= 100 {
  if score >= 90 {
print("A")
  } else if score >= 80 {
print("B")
  } else if score >= 70 {
print("C")
  } else {
print("Below C")
  }
} else {
  print("Invalid score")
}

Swift Short Hand If…Else

Use the ternary operator condition ? a : b for concise conditional expressions.

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Basic Ternary Operator

Use the ternary operator to choose between two values in a single expression.

Example

let age = 20
let status = (age >= 18) ? "Adult" : "Minor"
print(status)

This example returns “Adult” when age >= 18, otherwise “Minor”.

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REMOVE ADS

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Choose the Minimum

Use a ternary expression to select the smaller of two values.

Example

let a = 5, b = 9
let min = (a < b) ? a : b
print(min)

This prints the smaller number.

If a is not less than b, the expression returns b.