If and if-else statements in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of an if statement in Swift?

An if statement lets your program make decisions by running code only when a condition is true.

beginner

How does an if-else statement work?

It runs one block of code if the condition is true, and a different block if the condition is false.

beginner

What will this Swift code print?<br><pre>let age = 18
if age >= 18 {
  print("Adult")
} else {
  print("Minor")
}</pre>

It will print Adult because the age is 18, which meets the condition age >= 18.

beginner

Can an if statement run without an else?

Yes. You can use if alone to run code only when a condition is true, and do nothing if it is false.

intermediate

What is the syntax to check multiple conditions in Swift?

You can use else if between if and else to check more than one condition.

What does this Swift code do?

if temperature > 30 {
  print("Hot")
} else {
  print("Cool")
}

A Does nothing

B Always prints "Hot"

C Prints "Cool" if temperature is more than 30

D Prints "Hot" if temperature is more than 30, otherwise prints "Cool"

The if checks if temperature is greater than 30. If true, it prints "Hot"; otherwise, it prints "Cool".

Which keyword starts a condition check in Swift?

A when

B check

C if

D condition

The keyword if is used to start a condition check.

What happens if the if condition is false and there is no else?

A Nothing happens, the program skips the <code>if</code> block

B The code inside <code>if</code> runs anyway

C The program crashes

D The program asks for input

If the condition is false and there is no else, the program skips the if block and continues.

How do you check multiple conditions in Swift?

A Using multiple <code>if</code> statements only

B Using <code>else if</code> between <code>if</code> and <code>else</code>

C Using <code>switch</code> only

D Using <code>for</code> loops

You use else if to check multiple conditions in sequence.

What will this code print?

let score = 75
if score >= 90 {
  print("A")
} else if score >= 80 {
  print("B")
} else {
  print("C")
}

A "C"

B "A"

C "B"

D Nothing

Since 75 is less than 80, it does not meet the first two conditions, so it prints "C".

Explain how an if-else statement helps a program make decisions.

Think about choosing between two paths based on a yes/no question.

Write a simple Swift if statement that prints "Good morning" if a variable hour is less than 12.

Use the <code>if</code> keyword and a comparison operator.

Practice

1. What does an if statement do in Swift?

easy

A. It runs code only if a condition is true.

B. It repeats code multiple times.

C. It stores data in a variable.

D. It defines a new function.

Solution

1. Step 1: Understand the purpose of if statement

   An if statement checks a condition and runs code only when that condition is true.

2. Step 2: Compare with other options

   Repeating code is done by loops, storing data is done by variables, and defining functions uses func.

3. Final Answer:

   It runs code only if a condition is true. -> Option A

4. Quick Check:

   If statement = runs code if true [OK]

Hint: If checks true condition to run code, else skips it [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if stores data
• Mixing if with function definitions

2. Which of the following is the correct syntax for an if-else statement in Swift?

easy

A. if condition { } else { }

B. if (condition) then { } else { }

C. if condition then { } else { }

D. if condition: { } else: { }

Solution

1. Step 1: Recall Swift if-else syntax

   Swift uses if condition { } and else { } blocks without extra keywords like 'then' or colons.

2. Step 2: Check each option

   if condition { } else { } matches Swift syntax exactly. Options A, B, and C use invalid keywords or punctuation.

3. Final Answer:

   if condition { } else { } -> Option A

4. Quick Check:

   Swift if-else = if condition { } else { } [OK]

Hint: Swift uses braces {} without 'then' or colons in if-else [OK]

Common Mistakes:

• Adding 'then' keyword
• Using colons after if or else
• Putting condition in parentheses unnecessarily

3. What will be printed by this Swift code?

let number = 10
if number > 5 {
    print("Big")
} else {
    print("Small")
}

medium

A. Small

B. No output

C. 10

D. Big

Solution

1. Step 1: Evaluate the condition

   The variable number is 10. The condition number > 5 is true because 10 is greater than 5.

2. Step 2: Determine which block runs

   Since the condition is true, the code inside the if block runs, printing "Big".

3. Final Answer:

   Big -> Option D

4. Quick Check:

   10 > 5 is true, so prints "Big" [OK]

Hint: Check condition true? Run if block, else run else block [OK]

Common Mistakes:

• Confusing which block runs
• Printing variable instead of string
• Ignoring condition result

4. Find the error in this Swift code:

let age = 18
if age >= 18
    print("Adult")
else
    print("Minor")

medium

A. Variable age should be a string

B. Wrong comparison operator

C. Missing braces { } around if and else blocks

D. No error, code is correct

Solution

1. Step 1: Check Swift if-else syntax

   Swift requires braces { } around the code blocks after if and else.

2. Step 2: Identify missing braces

   The code lacks braces after if age >= 18 and else, causing a syntax error.

3. Final Answer:

   Missing braces { } around if and else blocks -> Option C

4. Quick Check:

   Swift needs braces for if-else blocks [OK]

Hint: Always use { } after if and else in Swift [OK]

Common Mistakes:

• Omitting braces in if-else
• Using wrong operators
• Wrong variable types

5. You want to write Swift code that prints "Positive", "Negative", or "Zero" depending on the value of an integer variable num. Which code correctly uses if-else statements to do this?

hard

A. if num >= 0 {
print("Positive")
} else if num <= 0 {
print("Negative")
} else {
print("Zero")
}

B. if num > 0 {
print("Positive")
} else if num < 0 {
print("Negative")
} else {
print("Zero")
}

C. if num > 0 {
print("Positive")
} else {
print("Negative")
}
print("Zero")

D. if num == 0 {
print("Zero")
} else if num > 0 {
print("Negative")
} else if num < 0 {
print("Positive")
}

Solution

1. Step 1: Understand the conditions needed

   We need to check if num is greater than 0, less than 0, or exactly 0.

2. Step 2: Analyze each option

   if num > 0 { print("Positive") } else if num < 0 { print("Negative") } else { print("Zero") } correctly checks >0, then <0, else zero. if num >= 0 { print("Positive") } else if num <= 0 { print("Negative") } else { print("Zero") } wrongly overlaps conditions. if num > 0 { print("Positive") } else { print("Negative") } print("Zero") prints "Zero" always. if num == 0 { print("Zero") } else if num > 0 { print("Negative") } else if num < 0 { print("Positive") } incorrectly prints "Negative" for positive numbers and "Positive" for negative numbers.

3. Final Answer:

   if num > 0 { print("Positive") } else if num < 0 { print("Negative") } else { print("Zero") } -> Option B

4. Quick Check:

   Check >0, else if <0, else zero [OK]

Hint: Check positive first, then negative, else zero last [OK]

Common Mistakes:

• Overlapping conditions causing wrong output
• Printing zero outside else block
• Wrong order of conditions