If–else statement in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested if–else statements

What is the output of this C++ code snippet?

C++

#include <iostream>
int main() {
    int x = 10;
    if (x > 5) {
        if (x < 15) {
            std::cout << "A";
        } else {
            std::cout << "B";
        }
    } else {
        std::cout << "C";
    }
    return 0;
}

A No output

B B

C A

D C

💡 Hint

Check the conditions step by step starting from the outer if.

x is 10, which is greater than 5, so the outer if is true. Then, x is less than 15, so the inner if is true, printing 'A'.

❓ Predict Output

intermediate

Output with else if ladder

What will this program print?

C++

#include <iostream>
int main() {
    int score = 75;
    if (score >= 90) {
        std::cout << "A";
    } else if (score >= 80) {
        std::cout << "B";
    } else if (score >= 70) {
        std::cout << "C";
    } else {
        std::cout << "F";
    }
    return 0;
}

A A

B B

C F

D C

💡 Hint

Check which condition the score satisfies first.

Score is 75, which is not >= 90 or >= 80, but is >= 70, so it prints 'C'.

❓ Predict Output

advanced

Output of if–else with logical operators

What is the output of this code?

C++

#include <iostream>
int main() {
    int a = 5, b = 10;
    if (a > 0 && b < 5) {
        std::cout << "X";
    } else if (a > 0 || b < 5) {
        std::cout << "Y";
    } else {
        std::cout << "Z";
    }
    return 0;
}

A Y

B X

C Z

D No output

💡 Hint

Evaluate the logical conditions carefully.

a > 0 is true, b < 5 is false, so first if is false (true && false = false). Second condition is true (true || false = true), so prints 'Y'.

❓ Predict Output

advanced

Value of variable after if–else execution

What is the value of variable result after running this code?

C++

#include <iostream>
int main() {
    int x = 3, result = 0;
    if (x % 2 == 0) {
        result = 10;
    } else {
        result = 20;
    }
    std::cout << result;
    return 0;
}

A 20

B 0

C 10

D Compilation error

💡 Hint

Check if x is even or odd.

x is 3, which is odd, so else block runs setting result to 20.

❓ Predict Output

expert

Behavior of if–else without braces

What will be the output of this code snippet?

C++

#include <iostream>
int main() {
    int x = 0;
    if (x == 0)
        std::cout << "Zero";
    std::cout << "Done";
    else
        std::cout << "Not zero";
    return 0;
}

A Zero

B Compilation error

C Not zero

D ZeroDone

💡 Hint

Without braces, 'if' controls only the next single statement, and an extra statement before 'else' causes a syntax error.

This code causes a compilation error ('else' without a previous 'if'). Without braces, the 'if' controls only the first 'std::cout << "Zero";'. The next 'std::cout << "Done";' is unconditional and separates the 'if' from the 'else', making the 'else' unmatched.

Practice

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

easy

A. It defines a function.

B. It repeats a block of code multiple times.

C. It chooses between two paths based on a condition.

D. It declares a variable.

Solution

1. Step 1: Understand the purpose of if-else

   An if-else statement lets the program decide which block of code to run based on a condition.

2. Step 2: Compare with other options

   Repeating code is done by loops, functions define reusable code, and variables store data, so these are not correct.

3. Final Answer:

   It chooses between two paths based on a condition. -> Option C

4. Quick Check:

   If-else = choose path [OK]

Hint: If condition true, run if-block; else run else-block [OK]

Common Mistakes:

• Confusing if-else with loops
• Thinking if-else defines functions
• Mixing variable declaration with control flow

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

easy

A. if (x > 0) { cout << "Positive"; } else { cout << "Non-positive"; }

B. if x > 0 then cout << "Positive" else cout << "Non-positive"

C. if (x > 0) cout << "Positive" else cout << "Non-positive";

D. if x > 0 { cout << "Positive" } else { cout << "Non-positive" }

Solution

1. Step 1: Check C++ if-else syntax rules

   C++ requires parentheses around the condition and braces around blocks for multiple statements.

2. Step 2: Analyze each option

   if (x > 0) { cout << "Positive"; } else { cout << "Non-positive"; } uses correct parentheses and braces. Options A and B miss parentheses or use incorrect keywords. if (x > 0) cout << "Positive" else cout << "Non-positive"; misses semicolon after else block.

3. Final Answer:

   if (x > 0) { cout << "Positive"; } else { cout << "Non-positive"; } -> Option A

4. Quick Check:

   Correct syntax uses parentheses and braces [OK]

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

Common Mistakes:

• Omitting parentheses around condition
• Missing braces for multiple statements
• Using 'then' keyword (not in C++)

3. What will be the output of this code?

int x = 5;
if (x < 3) {
  cout << "Less";
} else {
  cout << "More or equal";
}

medium

A. Less

B. More or equal

C. No output

D. Compilation error

Solution

1. Step 1: Evaluate the condition x < 3

   Variable x is 5, so 5 < 3 is false.

2. Step 2: Determine which block runs

   Since condition is false, the else block runs, printing "More or equal".

3. Final Answer:

   More or equal -> Option B

4. Quick Check:

   Condition false -> else block output [OK]

Hint: Check condition truth to pick if or else output [OK]

Common Mistakes:

• Assuming if-block runs when condition is false
• Confusing output strings
• Ignoring else block

4. Find the error in this code snippet:

int n = 10;
if n > 5 {
  cout << "Big";
} else {
  cout << "Small";
}

medium

A. Missing parentheses around condition

B. Missing semicolon after cout statements

C. Incorrect else keyword

D. Variable n not declared

Solution

1. Step 1: Check if statement syntax

   C++ requires parentheses around the condition in if statements.

2. Step 2: Identify the error

   The code uses if n > 5 without parentheses, which is invalid syntax.

3. Final Answer:

   Missing parentheses around condition -> Option A

4. Quick Check:

   if condition needs parentheses [OK]

Hint: Always put condition inside parentheses in if [OK]

Common Mistakes:

• Omitting parentheses in if condition
• Forgetting semicolons (though not the main error here)
• Misreading else keyword

5. You want to write a program that prints "Even" if a number is divisible by 2, otherwise prints "Odd". Which code correctly uses if-else to do this?

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 divisibility by 2

   A number is divisible by 2 if remainder when divided by 2 is zero, i.e., num % 2 == 0.

2. Step 2: Check each option's condition

   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. 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 D

4. Quick Check:

   Use modulo == 0 for even check [OK]

Hint: Use modulo (%) and == 0 to check even numbers [OK]

Common Mistakes:

• Using assignment (=) instead of comparison (==)
• Using division (/) instead of modulo (%)
• Reversing if and else blocks