How to convert a number from hexadecimal to binary in C++

#include <iostream>
using namespace std;
int main() {
  int i=0;
    char hex[10];
    cin>>hex;
    cout<<"The value in the binary form is = ";
    while(hex[i])
    {
        switch(hex[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':
            case 'a':
                cout<<"1010";
                break;
            case 'B':
            case 'b':
                cout<<"1011";
                break;
            case 'C':
            case 'c':
                cout<<"1100";
                break;
            case 'D':
            case 'd':
                cout<<"1101";
                break;
            case 'E':
            case 'e':
                cout<<"1110";
                break;
            case 'F':
            case 'f':
                cout<<"1111";
                break;
            default:
                cout<<"--Invalid Hex Digit ("<< hex[i] <<")--";
        }
        i++;
    }
  return 0;
}