Using return value of cin to take unknown number of inputs in C++

Consider a problem where we need to take an unknown number of integer inputs.

A typical solution is to run a loop and stop when a user enters a particular value. How to do it if we are not allowed to use if-else, switch-case and conditional statement.

The idea is to use the fact that ‘cin >> input’ false if non-numertic value is given. Note that this above approach holds true only when input value’s data type is int (integer).

Important Point : cin is an object if std::istream. In C++11 and later, std::istream has a conversion function explicit bool() const;, meaning that there is a valid conversion from std::istream to bool, but only where explicitly requested. An if or while counts as explicitly requesting a conversion to bool. [Source StackOVerflow]
Before C++ 11, std::istream had a conversion to operator void*() const;

// CPP program to take unknown number
// of integers from user.
#include <iostream>
using namespace std;
int main()
{
    int input; 
    int count = 0; 
    cout << "To stop enter any character";
    cout << "\nEnter Your Input::";

    // cin returns false when a character
    // is entered
    while (cin >> input) 
        count++; 
    
    cout << "\nTotal number of inputs entered: " 
         << count;
    return 0;
}

Output:

To stop enter any character
Enter Your Input 1 2 3 s
Total number of inputs entered: 3

This article is contributed by Aditya Rakhecha. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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