Swift Control Flow

In Swift, the if statement is used to execute a block of code based on the evaluation of one or more conditions. This type of statement is often referred to as a branch statement. It allows the program to “branch” and execute specific blocks of code when certain conditions are met.

For example, consider a real-life scenario: you plan to visit a market, and your parent instructs you, “If the plastic containers are on sale, buy two containers.” This is a conditional statement where the action, “buy two containers,” will only occur if the condition, “plastic containers are on sale,” is true.

Conditional statements are essential in programming as they help introduce logic and decision-making into the code.

Syntax:

if (condition) {
    // Body of the if statement
}

• The if statement evaluates the condition inside the parentheses ().
• If the condition evaluates to true, the block of code inside the curly braces {} is executed.
• If the condition evaluates to false, the block of code is skipped, and the control moves to the next statement.

Example 1: Basic if Statement

// Swift program demonstrating the if statement

let val = 30

// Checking if the number is greater than zero
if (val > 0) {
    // Body of the if statement
    print("The given number is positive.")
}

// Statement after the if statement (always executed)
print("Learning if statement in Swift.")

Output:

The given number is positive.
Learning if statement in Swift.

Explanation:

• A variable val is declared with a value of 30.
• The condition val > 0 is evaluated. Since 30 > 0, the condition is true.
• The code inside the if block is executed, printing: "The given number is positive."
• The statement after the if block, "Learning if statement in Swift.", is executed regardless of the condition’s result.
• If val were set to -20, the condition would be false, and only the statement outside the if block would be executed.

Example 2: Checking Eligibility

This person is eligible for voting.
Only 18+ people are eligible for voting.

Output:

Integer Type        Min                    Max
UInt8               0                     255
UInt16              0                     65535
UInt32              0                     4294967295
UInt64              0                     18446744073709551615
Int8               -128                   127
Int16              -32768                 32767
Int32              -2147483648            2147483647
Int64              -9223372036854775808   9223372036854775807

Example 3: Using Multiple if Statements

You can use multiple if statements to check independent conditions instead of using if-else.

// Swift program demonstrating multiple if statements

let number = 9

// First condition
if (number % 2 == 0) {
    print("\(number) is an even number")
}

// Second condition
if (number % 2 != 0) {
    print("\(number) is an odd number")
}

// Third condition
if (number == 9) {
    print("Given number \(number) is equal to the given condition number")
}

Output:

9 is an odd number
Given number 9 is equal to the given condition number

Explanation:

• The first if checks if the number is even (number % 2 == 0), which is false for 9, so this block is skipped.
• The second if checks if the number is odd (number % 2 != 0), which is true for 9, so it prints: "9 is an odd number."
• The third if checks if the number equals 9, which is true, so it prints: "Given number 9 is equal to the given condition number."

In Swift, the if-else statement is used to execute a block of code based on a condition and provide an alternative block of code to execute when the condition is not met. This allows programmers to handle conditional logic effectively, ensuring that the program can make decisions dynamically.

For example, imagine you’re at the market, and your parent says, “If biscuits are on sale, buy biscuits; otherwise, buy chips.” This is a typical if-else condition where one action is executed if the condition is true, and an alternative action is executed if the condition is false.

Syntax of the if-else Statement

if (condition) {
    // Body of the if statement
} else {
    // Body of the else statement
}

• The if condition is evaluated.
• If the condition evaluates to true, the code inside the if block is executed.
• If the condition evaluates to false, the code inside the else block is executed.
• The program then continues with the code after the if-else block.

Examples:

// Swift program to demonstrate the use of if-else statement

// Declare and initialize a variable
let val = 40

// Check if the number is equal to 40
if (val == 40) {
    print("Both the numbers are equal")
} else {
    print("Both the numbers are not equal")
}

// Code after if…else statement
// This statement is always executed
print("Learning if…else statement in Swift.")

Output:

Both the numbers are equal
Learning if…else statement in Swift.

Explanation:

• The variable val is initialized with a value of 40.
• The condition val == 40 evaluates to true, so the code inside the if block is executed, printing: "Both the numbers are equal".
• The else block is skipped.
• The statement after the if-else block, "Learning if…else statement in Swift.", is executed regardless of the condition.
• If val were set to 45, the condition would evaluate to false, and the output would change to:

Both the numbers are not equal
Learning if…else statement in Swift.

Example 2: Checking Voting Eligibility

// Swift program to demonstrate the use of if-else statement

// Declare and initialize a variable
let age = 80

// Checking if age is greater than or equal to 18
if (age >= 18) {
    print("This person is eligible for voting")
} else {
    // Executes when the condition is false
    print("This person is not eligible for voting")
}

// Code after if…else statement
print("Only 18+ people are eligible for voting")

Output:

This person is eligible for voting
Only 18+ people are eligible for voting

Explanation:

• The variable age is initialized with 80.
• The condition age >= 18 evaluates to true, so the code inside the if block is executed, printing: "This person is eligible for voting".
• The else block is skipped.
• The final statement after the if-else block is executed: "Only 18+ people are eligible for voting".
• If age were set to 16, the output would be:

This person is not eligible for voting
Only 18+ people are eligible for voting

In Swift, the if-else if-else statement allows you to evaluate multiple conditions and execute the code block corresponding to the first true condition. If none of the conditions are satisfied, the else block executes by default.

Syntax

if (condition1) {
    // Block of code for condition1
} else if (condition2) {
    // Block of code for condition2
} else if (condition3) {
    // Block of code for condition3
}
.
.
.
else {
    // Block of code for all other cases
}

• The program checks each condition in sequence.
• The first condition that evaluates to true will execute its associated block of code.
• If none of the conditions are true, the else block is executed.

Example 1: Grading System

let number = 85

if (number >= 90) {
    print("Grade A")
} else if (number >= 75) {
    print("Grade B")
} else if (number >= 60) {
    print("Grade C")
} else {
    print("Grade D")
}

Output:

Grade B

Explanation:

• The variable number is assigned the value 85.
• The first condition, number >= 90, evaluates to false.
• The second condition, number >= 75, evaluates to true.
• The program executes the code block associated with number >= 75, printing: "Grade B".
• No further conditions are evaluated because one has already been satisfied.

Example 2: Checking Specific Values

let number = 20

// Condition 1
if (number == 10) {
    print("Number is 10")
}
// Condition 2
else if (number == 15) {
    print("Number is 15")
}
// Condition 3
else if (number == 20) {
    print("Number is 20")
}
// Default case
else {
    print("Number is not present")
}

Output:

Number is 20

Explanation:

• The variable number is initialized with the value 20.
• The first condition, number == 10, evaluates to false.
• The second condition, number == 15, also evaluates to false.
• The third condition, number == 20, evaluates to true, so the corresponding code block executes, printing: "Number is 20".

In Swift, a nested if-else statement occurs when an if or else block contains another if-else statement inside it. This structure is used when multiple levels of conditions need to be checked. The outer if condition determines if the inner if-else will be executed.

Syntax:

// Outer if condition
if (condition1) {
    // Inner if condition
    if (condition2) {
        // Block of Code for condition2
    } else {
        // Block of Code if condition2 is false
    }
} else {
    // Inner if condition
    if (condition3) {
        // Block of Code for condition3
    } else {
        // Block of Code if condition3 is false
    }
}

• If condition1 is true, the outer if block is executed, and the program checks condition2.
• If condition1 is false, the program moves to the outer else block and evaluates condition3.
• Additional layers of if-else can be added as needed.

Example 1: Finding the Greatest Value

import Swift

var a = 100
var b = 200
var c = 300

// Outer if statement
if (a > b) {
    // Inner if statement
    if (a > c) {
        // Statement 1
        print("100 is Greater")
    } else {
        // Statement 2
        print("300 is Greater")
    }
} else {
    // Inner if statement
    if (b > c) {
        // Statement 3
        print("200 is Greater")
    } else {
        // Statement 4
        print("300 is Greater")
    }
}

Output:

300 is Greater

Explanation:

1. The outer if condition checks whether a > b. Since 100 > 200 is false, the program skips to the else block.
2. Inside the else block, the inner if checks whether b > c. Since 200 > 300 is also false, the program executes the inner else block.
3. The inner else block prints “300 is Greater” because c has the highest value.

Example 2: Checking Number Properties

import Swift

var number = 5

// Outer if statement
if (number >= 0) {
    // Inner if statement
    if (number == 0) {
        // Statement 1
        print("Number is 0")
    } else {
        // Statement 2
        print("Number is greater than 0")
    }
} else {
    // Statement 3
    print("Number is smaller than 0")
}

Output:

Number is greater than 0

In general, loops are used for iteration, which means repeating a set of instructions. With loops, we can execute tasks multiple times, as required. A loop can run indefinitely until its specified condition is no longer satisfied. Typically, we define a condition to terminate the loop. For instance, if we want to display “Hello World” 100 times, we use a loop and specify a condition such as n <= 100. The loop will terminate when the condition is no longer met.

Types of Loops in Swift

1. for-in loop
2. while loop
3. repeat-while loop

1. for-in Loop: The for-in loop is used for iterating over a sequence, such as arrays, dictionaries, ranges, or sets. Unlike an if statement, which executes a block of code only once if a condition is met, the for-in loop repeatedly executes the block as long as the condition is satisfied.

Syntax:

for item in range {
    // Statements
}

Example:

// Swift program to find if a number is a perfect number

// Declaring variables
var number = 6
var sum = 0

// Iterating to find divisors of the number
for i in 1...(number - 1) {
    if number % i == 0 {
        sum += i
    }
}

// Checking if the sum equals the number
if sum == number {
    print("The given number is a perfect number")
} else {
    print("The given number is not a perfect number")
}

Output:

The given number is a perfect number

2. While Loop: while loop repeatedly executes a block of code as long as the specified condition evaluates to true. Unlike the for-in loop, the while loop requires explicit initialization, condition checking, and variable updates.

Syntax:

while condition {
    // Statements
    increment/decrement
}

Example:

// Swift program to calculate the factorial of a number

// Declaring variables
var num = 5
var factorial = 1
var i = 1

// Iterating to calculate factorial
while i <= num {
    factorial *= i
    i += 1
}

print("The factorial of the given number is \(factorial)")

Output:

The factorial of the given number is 120

3. Repeat-While Loop: The repeat-while loop, similar to the do-while loop in C, executes the block of code at least once before evaluating the condition. It is also referred to as an exit-controlled loop.

Syntax:

repeat {
    // Statements
} while condition

Example:

// Swift program to demonstrate repeat-while loop

// Declaring variables
var start = 1
let limit = 10

// Iterating using repeat-while loop
repeat {
    print(start)
    start += 1
} while start <= limit

Output:

1
2
3
4
5
6
7
8
9
10

The break statement is a control statement used to immediately terminate the execution of the current loop or switch statement. When the break condition is met, the loop stops its iterations, and control passes to the first statement following the loop. In simpler terms, the break statement halts the current program flow based on specified conditions. It can be used within loops or switch statements to terminate execution earlier, especially when the number of iterations isn’t predetermined or depends on dynamic conditions.

Syntax:

break

1. for-in Loop: The for-in loop in Swift iterates over a sequence, such as a range, array, or string. The break statement can terminate the loop when a specific condition is satisfied.

Syntax:

for item in sequence {
    // Code block
    if condition {
        break
    }
}

Example:

// Swift program demonstrating the use of break in a for-in loop

print("Numbers in the range:")

// Loop from 1 to 10
for number in 1...10 {
    if number == 7 {
        break
    }
    print(number)
}

Output:

Numbers in the range:
1
2
3
4
5
6

2. While Loop: The while loop runs as long as the given condition is true. The break statement can be used to terminate the loop based on an additional condition.

Syntax:

while condition {
    // Code block
    if condition {
        break
    }
}

Example:

// Swift program demonstrating the use of break in a while loop

var count = 1

// Loop to print the first 4 multiples of 3
while count <= 10 {
    print("3 x \(count) = \(3 * count)")
    if count == 4 {
        break
    }
    count += 1
}

Output:

3 x 1 = 3
3 x 2 = 6
3 x 3 = 9
3 x 4 = 12

3. Nested Loops: The break statement can also be used in nested loops to terminate only the inner loop or control the flow of nested structures.

Syntax:

for item1 in sequence1 {
    for item2 in sequence2 {
        if condition {
            break
        }
    }
}

Example:

// Swift program demonstrating break in nested loops

for outer in 1...3 {
    for inner in 1...3 {
        if outer == 2 {
            break
        }
        print("Outer: \(outer), Inner: \(inner)")
    }
}

Output:

Outer: 1, Inner: 1
Outer: 1, Inner: 2
Outer: 1, Inner: 3
Outer: 3, Inner: 1
Outer: 3, Inner: 2
Outer: 3, Inner: 3