/* 
 * Add 1 to a natural x - Test with and without recursion.
 * Author: Gil Mendes (gil0mendes)
 *
 * Created on 11 de Julho de 2012, 18:34
 */

#include <cstdlib>
#include <iostream>

#include <time.h>

using namespace std;

/**
 * Add 1 to a natural x.
 * 
 * Function without recursion, very optimized.
 * By Gil Mendes (gil0mendes)
 * 
 * @param int64_t number - Natural number (x)
 * @return int64_t - Result
 */
int64_t add1ToX(register int64_t number) {
    register int64_t total = 0;

    do {
        total += number--;
    } while (number != 0);

    return total;
}

/**
 * Add 1 to natural x (with recursion)
 * 
 * By Luciana Sondermann
 * 
 * @param int n - Natural number (x)
 * @return int - Result
 */
int SomatRec(int n) {
    int soma;
    if (n == 1) {
        soma = 1;
    } else {
        soma = n + SomatRec(n - 1);
    }
    return soma;
}

void printResults(int64_t number, int64_t result, clock_t start, clock_t end) {
    cout << "The sum of 1 to " << number << " is: " << result << endl;
    cout << "Elapsed time (in microseconds): " << (end - start) << endl;
    
    return;
}

/*
 * Entry point of the program, tests the time between with and without recursion.
 */
int main(int argc, char** argv) {
    int64_t number = 0, result = 0;
    clock_t start, end;

    while (number <= 0) {
        cout << "Enter a natural number: ";
        cin >> number;
    }

    cout << endl << "Without recursion" << endl;
    start = clock();
    result = add1ToX(number);
    end = clock();
    printResults(number, result, start, end);
    
    cout << endl << "With recursion" << endl;
    start = clock();
    result = SomatRec(number);
    end = clock();
    printResults(number, result, start, end);

    return 0;
}

Code used to test the differences between "sum up a natural x 1", with or without recursion.

Add 1 to a natural x.

C++