Program to Find the Sum of Numbers in a Given Range in C++

Sum of Numbers in a Given Range

Given two integer inputs num1 and num2, the objective is to find the sum of all numbers in the given range using C++ programming.

We will explore different methods to achieve this.

Method 1: Using a for Loop

We iterate from num1 to num2, adding each number to a sum variable.

#include <iostream>
using namespace std;

int main() {
    int num1, num2, sum = 0;
    cout << "Enter the range (num1 num2): ";
    cin >> num1 >> num2;
    
    for (int i = num1; i <= num2; i++) {
        sum += i;
    }
    
    cout << "Sum of numbers in given range: " << sum;
    return 0;
}
            

Output:

Enter the range (num1 num2): 2 4
Sum of numbers in given range: 9

Method 2: Using the Formula

We use the formula for the sum of the first n natural numbers: sum = n(n+1)/2. Using this, we derive:

sum = (num2 * (num2 + 1) / 2) - ((num1 - 1) * num1 / 2)

#include <iostream>
using namespace std;

int main() {
    int num1, num2;
    cout << "Enter the range (num1 num2): ";
    cin >> num1 >> num2;
    
    int sum = (num2 * (num2 + 1) / 2) - ((num1 - 1) * num1 / 2);
    
    cout << "Sum of numbers in given range: " << sum;
    return 0;
}
            

Output:

Enter the range (num1 num2): 2 4
Sum of numbers in given range: 9

Method 3: Using Recursion

We use recursion to sum numbers from num1 to num2.

#include <iostream>
using namespace std;

int getSum(int num1, int num2) {
    if (num1 > num2) {
        return 0;
    }
    return num1 + getSum(num1 + 1, num2);
}

int main() {
    int num1, num2;
    cout << "Enter the range (num1 num2): ";
    cin >> num1 >> num2;
    
    cout << "Sum of numbers in given range: " << getSum(num1, num2);
    return 0;
}
            

Output:

Enter the range (num1 num2): 2 4
Sum of numbers in given range: 9