using input redirection in while loop - c++

Question

I need to create a program that reads in a list of random integers via input redirection and performs various tasks with them. For the purpose of this question I just want to print the sum of each number + 1. Trouble is, I don’t know how to get it to perform the operation on anything but the first number in the list. My mini program (program.cpp) is
#include <iostream>
using namespace std;
int main () {
int input;
bool arb = true;
cin >> input;
while (arb) {
cout << input + 1 << endl;
}
return 0;
}
and a sample textfile (textfile.txt) I'm using contains
9
8
7
6
When I run it it prints out “10” for infinity. What I’d like it do is print out
10
9
8
7
or the equivalent for whatever other text file may be used.
I thought maybe I could somehow reference specific lines in the textfile, but from searching how to do that all the similar questions I could find seemed to have solutions that required fstream, which is something I haven’t learned yet and therefore I’m not allowed to use it (this is for a class assignment).
The only compiler directives I’ve learned are iostream, string, cmath, iomanip, cstdlib, and ctime. The ways to get input I’ve learned are cin >> input, cin.get(input), and cin.getline(input), so if there are other ways of reading in the file besides those 3 that I’m unaware of, unfortunately I can’t use it. Note that my program HAS to use a while loop. The way the program will be run is
./program < whatevertextfile.txt
which I can't change.
given these restrictions, how can I get my program to read in and use each integer in the text file?

Answer 1

The idiomatic way to read a sequence of white-space separated integers in C++ would be
#include <iostream>
using namespace std;
int main () {
int input;
while (cin >> input) {
cout << input + 1 << endl;
}
return 0;
}
Let's come to why this works the way it does.
cin >> input
discards possible white-space and then reads an integer from the standard input. Moreover, it returns a reference of the cin object used. With this returned reference, you can call the bool conversion operator to check if any of the fail bits is set in the given std::basic_ios object. So
while (cin >> input)
does two things. Read an integer from standard input and check if it successfully completed the operation. As long as this operation succeeds, your while loop continues to iterate and you print the numbers.
See http://en.cppreference.com/w/cpp/io/basic_istream/operator_gtgt for reference on std::basic_istream::operator>>.
See http://en.cppreference.com/w/cpp/io/basic_ios/operator_bool for reference on operator bool.
Edit1: Move references to bottom so that the answer is more readable.