CPP Mid-Coding

Movie Ticket Pricing

Problem: A cinema charges $12 for adults (age >= 18), $8 for teens (13–17), and $5 for kids (< 13). The code crashes for some inputs.

Question: What’s wrong with the code?

• The variable price is not initialized and may be undefined.

• The condition age > 18 should be age >= 18

• The else if statements are in the wrong order

• The cout statement is outside the if block.

Answer explanation

If none of the conditions match (e.g., invalid age), price remains uninitialized, leading to undefined behavior. Add an else or initialize price:

Weather App Alert

Problem: A weather app alerts based on temperature: "Freezing" (< 0°C), "Cold" (0–10°C), "Mild" (> 10°C). The code has a syntax error.

Question: What’s wrong with the code?

• Nothing; the code is correct.

• The condition temp <= 10 should be temp < 10.

• Missing ; after cout statements.

• The temp variable should be a float.

Answer explanation

Explanation: The code is syntactically correct and logically sound. For temp = 5, it outputs "Cold" as expected.

Vending Machine Change

Problem: A vending machine returns change if payment > $5, dispenses the item if payment == $5, or requests more money otherwise. The logic fails.

Question: What’s the issue?

• The condition payment = 5 should use ==.

• The payment variable should be an int.

• The else if is unnecessary.

• The cout statements are incorrect.

Answer explanation

Explanation: The else if condition uses = (assignment) instead of == (comparison). Correct code:

Student Grade Calculator

Problem: A grading system assigns: A (>= 90), B (80–89), C (70–79), F (< 70). The code assigns incorrect grades.

Question: What’s wrong?

• The conditions should use >= instead of >.

• The grade variable is not initialized.

• The conditions are in the wrong order.

• The code is correct.

Answer explanation

Explanation: The conditions exclude boundary values (e.g., score = 90 gets B instead of A). Use >=:

Parking Fee Calculator

Problem: A parking lot charges $5 for <= 2 hours, $10 for 3–5 hours, $15 for > 5 hours. The code has a syntax error.

Question: What’s the issue?

• Missing semicolon ; after fee = 10.

• The fee variable is not initialized.

• The condition hours <= 5 is incorrect.

• The else if should be elif.

Answer explanation

Explanation: A missing ; after fee = 10 causes a syntax error. Correct code:

Online Shopping Discount

Problem: An online store offers 20% off for orders > $100, 10% for $50–100, and no discount for < $50. The discount is incorrect.

Question: What’s wrong?

• The condition order > 50 should be order >= 50.

• The discount variable should be an int.

• The cout statement is incorrect.

• The code is correct.

Answer explanation

Explanation: The condition order > 50 excludes $50. Use >=:

Elevator Weight Limit

Problem: An elevator allows entry if weight <= 1000 lbs, warns if 1000–1200 lbs, and blocks if > 1200 lbs. The code has a syntax error.

Question: What’s the issue?

• Missing semicolon ; after cout << "Warning: Overweight" << endl.

• The condition weight <= 1200 is incorrect.

• The weight variable should be a double.

• The else if is invalid.

Answer explanation

Explanation: A missing ; after cout << "Warning: Overweight" << endl causes a syntax error. Correct code:

Library Fine System

Problem: A library charges $1/day for books overdue 1–7 days, $2/day for 8–14 days, $5/day for > 14 days. The fine is incorrect.

Question: What’s wrong?

• The fine for 8–14 days should account for the first 7 days.

• The fine variable is not initialized.

• The conditions are in the wrong order.

• The code is correct.

Answer explanation

Explanation: For 8–14 days, the fine should be $7 for the first 7 days plus $2/day for extra days. Correct code:

Coffee Shop Order

Problem: A coffee shop charges $3 for small, $5 for medium, $7 for large drinks. The code fails for some sizes.

Question: What’s the issue?

• The code is correct.

• The size variable should be a char.

• The else if condition is incorrect.

• The price variable is not initialized.

Answer explanation

Explanation: The code is correct. For size = "medium", it outputs $5.

Fitness Tracker

Problem: A fitness tracker categorizes heart rate: "Resting" (< 100 bpm), "Moderate" (100–140 bpm), "Intense" (> 140 bpm). The code has a syntax error.

Question: What’s the issue?

• Missing closing brace } after the second cout.

• The condition heart_rate <= 140 is incorrect.

• The else if should be elif.

• The heart_rate variable is undefined.

Answer explanation

Explanation: A missing } after cout << "Moderate" << endl; causes a syntax error. Correct code: