Reading digits and converting to words

I'm new to c++ and I have to write a program that takes a user 4-digit number and convert it to words i.e. 7238 would be wrote as seven two three eight. Yet it writes every number as unknown. Any advice for a noob would be greatly appreciated.

#include iostream

using namespace std;

int main() {


     char number;


    cout << "Please enter a 4 digit number: ";

     cin >> number;

        switch(number){

        case 1 :
            cout<< "one"; 
            break;
        case 2 :
            cout<< "two";
            break;
        case 3 :
            cout<< "three";
            break;
        case 4 :
            cout<< "four";
            break;
        case 5 :
            cout<< "five";
            break;
        case 6 :
            cout<< "six";
            break;
        case 7 :
            cout<< "seven";
            break;
        case 8 :
            cout<< "eight";
            break;
        case 9 :
            cout<< "nine";
            break;
        case 0 :
            cout<< "zero";
            break;

        default :
            cout << "UNKNOWN.";
   }

}