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

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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 statements?

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

Important Point: cin is an object of 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 conversion to bool. [Source StackOVerflow

Before C++ 11, std::istream had a conversion to operator void*() const;


// C++ 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 anything except integer";
    cout << "\nEnter Your Input::";
    // cin returns false when anything
    // is entered except integer
    while (cin >> input)
    cout << "\nTotal number of inputs entered: "
         << count;
    return 0;
//This code is updated by Susobhan Akhuli



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

Time Complexity: O(count)
Auxiliary Space: O(1)


Last Updated : 23 Jun, 2022
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