Answer:
Following are the program in c++
First code when using for loop 
#include<iostream> // header file  
using namespace std; // namespace
int main() // main method
{
int n, i, sum1 = 0; // variable declaration
cout<<"Enter the number: "; // taking the value of n  
cin>>n;
if(n > 0) // check if n is nonnegative
{
for(i=n; i<=(2*n); i++)
{
sum1+= i;
}
}
else //  check if n  is negative
{
for(i=(2*n); i<=n; i++)
{
sum1+= i;
}
}
cout<<"The sum is:"<<sum1;
return 0;
Output
Enter the number: 1
The sum is:3
second code when using while loop 
#include<iostream> // header file  
using namespace std; // namespace
int main() // main method
{
int n, i, sum1 = 0; // variable declaration
cout<<"Enter the number: "; // taking the value of n  
cin>>n;
if(n > 0) // check if n is nonnegative
{
int i=n;  
while(i<=(2*n))
{
sum1+= i;
i++;
}
}
else //  check if n  is negative
{
int i=n;  
while(i<=(2*n))
{
sum1+= i;
i++;
}
}
cout<<"The sum is:"<<sum1;
return 0;
}
Output
Enter the number: 1
The sum is:3
Explanation:
Here we making 2 program by using different loops but using same logic 
Taking a user input in "n" variable.
if n is nonnegative then we iterate the loops  n to 2 * n and storing the sum in "sum1" variable.
Otherwise iterate a loop  2 * n to n and storing the sum in "sum1" variable.  Finally display  sum1 variable .