User input validation using "cin"

Question

I need to validate the user input through cin my code is as below :

#include"iostream"
using namespace std;

int main()
{
int choice = 0; 
while(1)
{
    cout<<"ENTER your choice a value between 0 to 2"<<endl;
        cin>>choice;    

        // Here i need some logic which will work like "choice" can be only
        // Integer and within the range i.e. 0 to 2 and if it is not
    // satisfy condition then ask user to input again
    switch(choice)
    {
    case 0:
        exit(1);
        break;

    case 1:
       fun();
       break;
    case 2:
       fun1();
       break;
    default: cout<<"Please enter a valid value"<<endl;
            break;
    }
}

return 0;

}

This might help: parashift.com/c++-faq/istream-and-ignore.html — Qaz
– Qaz, Commented Jan 13, 2013 at 14:27
You haven’t really explained what the problem is (but see chris’ comment). Also, while (1) => while (true) and I’d replace exit(1) by return 1. — Konrad Rudolph
– Konrad Rudolph, Commented Jan 13, 2013 at 14:29
@KonradRudolph yeah that i can do and chris comment i checked i think that will resolve my problem....i need just a user input from 0 to 2 and reject other inputs and to angin ask from user for the input. — Astro - Amit
– Astro - Amit, Commented Jan 13, 2013 at 14:31

masoud · Accepted Answer · 2013-10-15 18:25:52Z

1

A simple sample:

#include <iostream>
#include <string>
#include <sstream>
using namespace std;

template <typename T>
bool toNumber(const std::string &x, T &num)
{
    return (std::stringstream(x) >> num);
}
int main() {
    while (true) {
        cout << "ENTER your choice a value between 0 to 2" << endl;

        string s;
        cin >> s;

        int choice = 0;

        if (toNumber(s, choice)) {
            switch (choice) {
              case 0: exit(1); break;
              case 1: fun();   break;
              case 2: fun1();  break;
            }
        }
        else
            cout << "Please enter a valid value" << endl;
    }
}

edited Oct 15, 2013 at 18:25

answered Jan 13, 2013 at 14:32

masoud

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