How to Reliably Input Numbers Using `cin` in C ?

Troubleshooting Number Input with cin

In C , the cin function can be used to read user input, but it becomes problematic when attempting to validate the input as a valid number. This issue arises when non-numeric characters are input, potentially leaving behind partial input for the next iteration.

One solution is to utilize std::getline and std::string to read the entire line of input. Subsequently, std::stringstream is employed to parse the input and extract a double value. The loop continues until the entire line can be successfully converted to a double, eliminating the issue of leftover input.

#include <string>
#include <sstream>

int main()
{
    std::string line;
    double d;
    while (std::getline(std::cin, line))
    {
        std::stringstream ss(line);
        if (ss >> d)
        {
            if (ss.eof())
            {   // Success
                break;
            }
        }
        std::cout << "Error!" << std::endl;
    }
    std::cout << "Finally: " << d << std::endl;
}

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