C++ Recursion: Sum of prime numbers in a range

Last update on December 20 2024 12:25:14 (UTC/GMT +8 hours)

Write a C++ program to implement a recursive function to find the sum of all prime numbers in a given range.

Sample Solution:

C Code:

#include <iostream>

// Recursive function to check if a number is prime
bool isPrime(int number, int divisor = 2)
{
    // Base cases
    if (number <= 2)
        return (number == 2);
    if (number % divisor == 0)
        return false;
    if (divisor * divisor > number)
        return true;

    // Recursive case: check if the number is divisible by the next divisor
    return isPrime(number, divisor + 1);
}

// Recursive function to find the sum of all prime numbers in a range
int sumOfPrimes(int start, int end)
{
    // Base case: if the start becomes greater than the end, stop the recursion
    if (start > end)
        return 0;

    // Recursive case: if the current number is prime, add it to the sum
    int sum = isPrime(start) ? start : 0;

    // Recursively call the function with the next number in the range
    return sum + sumOfPrimes(start + 1, end);
}

int main()
{
    int start, end;
    std::cout << "Input the starting number: ";
    std::cin >> start;
    std::cout << "Input the ending number: ";
    std::cin >> end;

    // Calculate the sum of prime numbers using recursion
    int sum = sumOfPrimes(start, end);

    std::cout << "Sum of prime numbers in the said range [" << start << ", " << end << "]: " << sum << std::endl;

    return 0;
}

Sample Output:

Input the starting number: 1
Input the ending number: 7
Sum of prime numbers in the said range [1, 7]: 17

Flowchart:

CPP Code Editor:

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Previous C++ Exercise: Checking if a binary tree is a binary search tree.