求用户提供的两个整数之间的整数的和

#include <iostream>

int main()

{

   std::cout <<"enter two numbers:"<<std::endl;

int v1,v2;

std::cin >>v1 >>v2;//read input

//use smaller number as lower bound for summation

//and larger number as upper bound

int lower,upper;

if (v1 <=v2){

  lower=v1;

  upper=v2;

}else{

lower=v2;

upper=v1;

}

int sum=0;

//sumvalues from lower up to and including upper

for (int val=lower;val<=upper;++val)

   sum+=val;//sum=sum+val

 std::cout<<"sum of"<<lower

      <<"to"<<upper

  <<"inclusive is"

   <<sum<<std::endl;

  return 0;

}