If statement in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of an if statement in C++?

An if statement lets the program decide to run some code only if a condition is true. It's like choosing a path based on a yes/no question.

beginner

Write the basic syntax of an if statement in C++.

The basic syntax is:

if (condition) {
  // code to run if condition is true
}

beginner

What happens if the condition in an if statement is false?

If the condition is false, the code inside the if block is skipped and the program continues with the next part.

beginner

How do you add an alternative action if the if condition is false?

You use an else block after the if. It runs when the if condition is false.

if (condition) {
  // if true
} else {
  // if false
}

intermediate

Can you check multiple conditions in C++? How?

Yes, by using else if blocks between if and else. It checks conditions one by one until one is true.

if (cond1) {
} else if (cond2) {
} else {
}

What does this code print?

int x = 5;
if (x > 3) {
  std::cout << "Yes";
} else {
  std::cout << "No";
}

A Error

B Yes

C Nothing

D No

Since 5 is greater than 3, the condition is true, so it prints "Yes".

Which keyword is used to provide an alternative when an if condition is false?

A else

B elif

C otherwise

D switch

In C++, else is used to run code when the if condition is false.

What will happen if the if condition is false and there is no else block?

A The code inside <code>if</code> is skipped

B The program will crash

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

D The program asks for input

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

How do you check multiple conditions in sequence?

A Using <code>for</code> loops

B Using multiple <code>if</code> statements without <code>else</code>

C Using <code>switch</code> only

D Using <code>else if</code> blocks

else if lets you check several conditions one after another.

Which of these is a valid if condition in C++?

A if x > 5 then { }

B if x > 5 { }

C if (x > 5) { }

D if (x > 5) then { }

In C++, conditions must be inside parentheses after if.

Explain how an if statement controls the flow of a program.

Think about making choices based on yes/no questions.

Describe the difference between if, else if, and else in C++.

Imagine checking multiple doors until one opens.

Practice

1. What does an if statement do in C++?

easy

A. Defines a new variable

B. Repeats code multiple times

C. Runs code only if a condition is true

D. Ends the program immediately

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, defining variables is done by declarations, and ending the program is done by return or exit.

3. Final Answer:

   Runs code only if a condition is true -> Option C

4. Quick Check:

   If statement = runs code if true [OK]

Hint: If checks true condition to run code [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if defines variables
• Believing if ends program

2. Which of the following is the correct syntax for an if statement in C++?

easy

A. if condition { cout << "Yes"; }

B. if condition: cout << "Yes";

C. if (condition) cout << "Yes"

D. if (condition) { cout << "Yes"; }

Solution

1. Step 1: Recall correct if syntax

   In C++, the condition must be inside parentheses and the code block inside curly braces.

2. Step 2: Check each option

   if (condition) { cout << "Yes"; } uses parentheses and curly braces correctly. if condition { cout << "Yes"; } misses parentheses. if condition: cout << "Yes"; uses colon which is invalid in C++. if (condition) cout << "Yes" misses curly braces which is allowed only for single statements but here it is incomplete.

3. Final Answer:

   if (condition) { cout << "Yes"; } -> Option D

4. Quick Check:

   Parentheses + braces = correct if syntax [OK]

Hint: Use parentheses for condition and braces for code [OK]

Common Mistakes:

• Missing parentheses
• Using colon instead of braces
• Omitting braces for multiple statements

3. What will be the output of this code?

int x = 10;
if (x > 5) {
  cout << "Hello";
} else {
  cout << "Bye";
}

medium

A. Hello

B. Bye

C. HelloBye

D. No output

Solution

1. Step 1: Evaluate the condition x > 5

   Since x is 10, which is greater than 5, the condition is true.

2. Step 2: Determine which block runs

   Because the condition is true, the code inside the if block runs, printing "Hello".

3. Final Answer:

   Hello -> Option A

4. Quick Check:

   10 > 5 is true, prints Hello [OK]

Hint: Check condition true or false to pick output [OK]

Common Mistakes:

• Confusing else output
• Ignoring condition result
• Assuming both blocks run

4. Find the error in this code snippet:

int a = 3;
if a > 0 {
  cout << "Positive";
}

medium

A. Missing semicolon after if

B. Condition must be inside parentheses

C. Missing curly braces

D. Variable a is not declared

Solution

1. Step 1: Check the if statement syntax

   The condition in an if statement must be inside parentheses.

2. Step 2: Identify the error

   The code writes if a > 0 { without parentheses, which is invalid syntax.

3. Final Answer:

   Condition must be inside parentheses -> Option B

4. Quick Check:

   If condition needs parentheses [OK]

Hint: Always put condition inside parentheses [OK]

Common Mistakes:

• Omitting parentheses
• Thinking semicolon needed after if
• Assuming braces optional always

5. You want to print "Even" if a number is even, and "Odd" if it is odd. Which code correctly uses an if statement to do this?

int num = 7;
// Your code here

hard

A. if (num % 2 == 0) { cout << "Even"; } else { cout << "Odd"; }

B. if (num / 2 == 0) { cout << "Even"; } else { cout << "Odd"; }

C. if (num % 2 = 0) { cout << "Even"; } else { cout << "Odd"; }

D. if (num % 2 != 0) { cout << "Even"; } else { cout << "Odd"; }

Solution

1. Step 1: Understand how to check even numbers

   A number is even if dividing by 2 leaves remainder 0, checked by num % 2 == 0.

2. Step 2: Analyze each option

   if (num % 2 == 0) { cout << "Even"; } else { cout << "Odd"; } correctly uses num % 2 == 0. if (num / 2 == 0) { cout << "Even"; } else { cout << "Odd"; } uses division instead of modulo, which is wrong. if (num % 2 = 0) { cout << "Even"; } else { cout << "Odd"; } uses assignment = instead of comparison ==. if (num % 2 != 0) { cout << "Even"; } else { cout << "Odd"; } reverses the logic.

3. Final Answer:

   if (num % 2 == 0) { cout << "Even"; } else { cout << "Odd"; } -> Option A

4. Quick Check:

   Modulo 2 equals 0 means even [OK]

Hint: Use modulo (%) to check evenness [OK]

Common Mistakes:

• Using division instead of modulo
• Using = instead of ==
• Reversing condition logic