Hexadecimal to Binary - C++ Program

#include<iostream>
using namespace std;
int main()
{
        long int i=0;
        char hexa[100];
        cout<<"\n Enter Hexadecimal Number : ";
        cin>>hexa;
        cout<<"\n Conversion of Hexadecimal Number to Binary Number : ";
        while(hexa[i])
        {
                switch(hexa[i])
                {
                        case '0' : cout<<"0000";
                                break;
                        case '1' : cout<<"0001";
                                break;
                        case '2' : cout<<"0010";
                                break;
                        case '3' : cout<<"0011";
                                break;
                        case '4' : cout<<"0100";
                                break;
                        case '5' : cout<<"0101";
                                break;
                        case '6' : cout<<"0110";
                                break;
                        case '7' : cout<<"0111";
                                break;
                        case '8' : cout<<"1000";
                                break;
                        case '9' : cout<<"1001";
                                break;
                        case 'A' : cout<<"1010";
                                break;
                        case 'B' : cout<<"1011";
                                break;
                        case 'C' : cout<<"1100";
                                break;
                        case 'D' : cout<<"1101";
                                break;
                        case 'E' : cout<<"1110";
                                break;
                        case 'F' : cout<<"1111";
                                break;
                        case 'a' : cout<<"1010";
                                break;
                        case 'b' : cout<<"1011";
                                break;
                        case 'c' : cout<<"1100";
                                break;
                        case 'd' : cout<<"1101";
                                break;
                        case 'e' : cout<<"1110";
                                break;
                        case 'f' : cout<<"1111";
                                break;
                        default : cout<<"\n Invalid Hexadecimal Digit... "<<hexa[i];
                }
                i++;
        }
        return 0;
}