// program to print the sum of all the numbers from the first to the second.
#include <iostream>
using namespace std;

int main()
{
   int first;
   int second;
   int current;
   int sum;
   
   cout << "Enter first number -- ";
   cin >> first;
   cout << "Enter second number -- ";
   cin >> second;

   // using a while loop
   sum = 0;
   current = first;
   while (current <= second) {
      sum = sum + current;
      current = current + 1;
   }
   cout << "The sum from "<< first << " to "<< second << " is "<< sum << endl;
   
   // using a do-while loop
   sum = 0;
   current = first;
   do {
      if (current <= second) {
	 sum = sum + current;
	 current++;
      }
   } while (current <= second);
   cout << "The sum from "<< first << " to "<< second << " is "<< sum << endl;

   // using a for loop
   sum = 0;
   for(current = first; current <= second; current++)
      sum = sum + current;
   cout << "The sum from "<< first << " to "<< second << " is "<< sum << endl;

   // without using current
   sum = 0;
   cout << "The sum from " << first << " to " << second;
   while (first <= second) {
      sum = sum + first;
      first = first + 1;
   }
   cout << " is " << sum << endl;

   return 0;
}