Catch character input in type number

[csstudent123]

Hi

int c;
cin>>c; //but user put character but want to tell user to enter non-char

how can I do this? thanks

[shadder]

you could use cin.fail() but then you also have to use cin.clear() and cin.ignore(500,'\n') somewhat like this

int c;
start:
cin>>c;
if(cin.fail())
    {
    cout<<"\nplease enter a int\n";
    cin.clear();
    cin.ignore(500,'\n');//500 is just a large  number  nothing special about it
    goto start;
    }

PS: Using goto is a bad practice

[MiiNiPaa]

Example program showing basic useful stuff like looping on input and stream state manipulation.

#include <iostream>
#include <limits>

int main()
{
    int x;
    std::cout << "Enter a number\n";
    while(not (std::cin >> x)) { //while error flag is set after input
        std::cout << "Invalid input\nPlease enter a number\n";
        std::cin.clear(); //clear error flags
        //skip all characters currently in buffer
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    }
    std::cout << "You entered " << x;
}

[andywestken]

If you want to tighten up the input code so the user is not allowed to enter values like "78kg" "99 red balloons", or "1 2 3 4", then it takes a bit more effort.

See this post for more info:

Trying to limit input to int type
http://www.cplusplus.com/forum/beginner/108849/#msg592118

Andy

#include <iostream>
#include <sstream>
#include <limits>

int main()
{
    int x = -1; // something other than 0

    do {
        bool notDone = true;

        while (notDone) {
            std::cout << "Enter a number (0 to quit)\n";

            std::string line;
            std::getline(std::cin, line); // read whole line

            std::istringstream is(line); // use string to init stringstream

            // try to extract an int (x) and, if successful, any non-whitechar
            // later on the line (should get just the int)
            char dummy = '\0';
            // if we fail to get an int or we successfully get something other
            // than whitespace
            if (!(is >> x) || (is >> std::ws && is.get(dummy)))
                std::cout << "Invalid input. Try again!\n";
            else
                notDone = false ;
        }
        std::cout << "You entered " << x << "\n";
    } while(0 != x);

    return 0;
}

Enter a number (0 to quit)
68kg
Invalid input. Try again!
Enter a number (0 to quit)
99 red balloons
Invalid input. Try again!
Enter a number (0 to quit)
1 2 3 4
Invalid input. Try again!
Enter a number (0 to quit)
42
You entered 42
Enter a number (0 to quit)
0
You entered 0

Cf. adding loop to MiiNiPaa's code:

#include <iostream>
#include <limits>

int main()
{
    int x = -1; // something other than 0

    do {
        std::cout << "Enter a number (0 to quit)\n";
        while(not (std::cin >> x)) { //while error flag is set after input
            std::cout << "Invalid input\nPlease enter a number\n";
            std::cin.clear(); //clear error flags
            //skip all characters currently in buffer
            std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
        }
        std::cout << "You entered " << x << "\n";
    } while(0 != x);

    return 0;
}

Enter a number (0 to quit)
68kg
You entered 68
Enter a number (0 to quit)
Invalid input
Please enter a number
99 red balloons
You entered 99
Enter a number (0 to quit)
Invalid input
Please enter a number
1 2 3 4
You entered 1
Enter a number (0 to quit)
You entered 2
Enter a number (0 to quit)
You entered 3
Enter a number (0 to quit)
You entered 4
Enter a number (0 to quit)
42
You entered 42
Enter a number (0 to quit)
0
You entered 0

[csstudent123]

Thanks all, :), I thought using try catch but this is better

[shadder]

Welcome :)

@andywestken The stuff you wrote were very cool, learnt a lot from it... Thanx :D