Practice Top 30 C++ Programming Questions on Recursion

Practice Top 30 C++ Programming Questions on Recursion

Q1 . Write a recursive function to calculate the factorial of a number.  
Input: 5  
Expected Output: 120

Q2. Write a recursive function to print the nth Fibonacci number.  
Input: 7  
Expected Output: 13

Q3. Write a recursive function to calculate the sum of digits of a number.  
Input: 1234  
Expected Output: 10

Q4. Write a recursive function to calculate base^exponent.  
Input: 2, 3  
Expected Output: 8

Q5. Write a recursive function to check if a string is a palindrome.  
Input: "radar"  
Expected Output: True

Q6. Write a recursive function to find the sum of all elements in an array.  
Input: {1, 2, 3, 4, 5}  
Expected Output: 15

Q7. Write a recursive function to reverse a string.  
Input: "hello"  
Expected Output: "olleh"

Q8. Write a recursive function to find the greatest common divisor (GCD) of two numbers.  
Input: 48, 18  
Expected Output: 6

Q9. Write a recursive function to print the binary representation of a number.  
Input: 10  
Expected Output: 1010

Q10. Write a recursive function to calculate the length of a string.  
Input: "recursion"  
Expected Output: 9

Q11. Write a recursive function to calculate the sum of the first N natural numbers.  
Input: 10  
Expected Output: 55

Q12. Write a recursive function to find the smallest element in an array.  
Input: {3, 1, 4, 1, 5}  
Expected Output: 1

Q13. Write a recursive function to count the number of digits in a number.  
Input: 4567  
Expected Output: 4

Q14. Write a recursive function to check if an array is sorted in ascending order.  
Input: {1, 2, 3, 4, 5}  
Expected Output: True

Q15. Write a recursive function to print numbers from N to 1 in reverse order.  
Input: 5  
Expected Output: 5 4 3 2 1

Q16. Write a recursive function to calculate combinations using the formula:  
\[
nCk = \frac{n!}{k!(n-k)!}
\]  
Input: 5, 2  
Expected Output: 10

Q17. Write a recursive function to find the largest element in an array.  
Input: {7, 3, 9, 2}  
Expected Output: 9

Q18. Write a recursive function to convert a decimal number to its octal representation.  
Input: 63  
Expected Output: 77

Q19. Write a recursive function to count occurrences of a specific number in an array.  
Input: {1, 2, 3, 2, 2}, 2  
Expected Output: 3

Q20. Write a recursive function to find the HCF of two numbers using the Euclidean algorithm.  
Input: 24, 36  
Expected Output: 12

Q21. Write a recursive function to calculate a^b using efficient exponentiation by squaring.  
Input: 3, 4  
Expected Output: 81

Q22. Write a recursive function to check whether a number is prime.  
Input: 29  
Expected Output: True

Q23. Write a recursive function to convert a numeric string to an integer.  
Input: "1234"  
Expected Output: 1234

Q24. Write a recursive function to replace all occurrences of a character in a string.  
Input: "hello", 'l', 'x'  
Expected Output: "hexxo"

Q25. Write a recursive function to convert a decimal number to its hexadecimal representation.  
Input: 255  
Expected Output: FF

Q26. Write a recursive function to calculate the sum of all even numbers in an array.  
Input: {1, 2, 3, 4, 5}  
Expected Output: 6

Q27. Write a recursive function to find the second largest element in an array.  
Input: {7, 5, 3, 1}  
Expected Output: 5

Q28. Write a recursive function to print all subsequences of a given string.  
Input: "abc"  
Expected Output: "a", "b", "c", "ab", "bc", "ac", "abc"

Q29. Write a recursive function to check whether a number is a perfect number.  
Input: 6  
Expected Output: True  
(Explanation: 6 = 1 + 2 + 3)

Q30. Write a recursive function to reverse an array.  
Input: {1, 2, 3, 4}  
Expected Output: {4, 3, 2, 1}