A logical extension of this program would be to ask the user to input a set of numbers to sum. In this case, we won’t know how many numbers to add. Instead, we’ll keep reading numbers until there are no more numbers to read

#include <iostream>
int main()
{
int sum = 0, value = 0;
// read until end-of-file, calculating a running total of all values read
while (std::cin >> value)
sum += value; // equivalent to sum = sum + value
std::cout << "Sum is: " << sum << std::endl;
return 0;
}

Output:

3 4 5 6
Sum is: 18