Convert hexadecimal into binary

HexToBinary.cpp

/*  HexToBinary Headerfile
	Convert Hexdata into binary
    (C) 2017, Staubgeborener
    https://github.com/Staubgeborener/ */

#include "HexToBinary.h"
#include <stdio.h>
#include <string.h>

HexToBinary::HexToBinary() {

}

char* HexToBinary::convert(char hexdec[])
{
    size_t n = strlen(hexdec) - 1;
    char buf[256];
    char value[4];
    for (int i = 0; i < n; i++) {
    {
         switch(hexdec[i])
         {
             case '0': strncpy(value, "0000", 4); break;
             case '1': strncpy(value, "0001", 4); break;
             case '2': strncpy(value, "0010", 4); break;
             case '3': strncpy(value, "0011", 4); break;
             case '4': strncpy(value, "0100", 4); break;
             case '5': strncpy(value, "0101", 4); break;
             case '6': strncpy(value, "0110", 4); break;
             case '7': strncpy(value, "0111", 4); break;
             case '8': strncpy(value, "1000", 4); break;
             case '9': strncpy(value, "1001", 4); break;
             case 'A': strncpy(value, "1010", 4); break;
             case 'B': strncpy(value, "1011", 4); break;
             case 'C': strncpy(value, "1100", 4); break;
             case 'D': strncpy(value, "1101", 4); break;
             case 'E': strncpy(value, "1110", 4); break;
             case 'F': strncpy(value, "1111", 4); break;
             case 'a': strncpy(value, "1010", 4); break;
             case 'b': strncpy(value, "1011", 4); break;
             case 'c': strncpy(value, "1100", 4); break;
             case 'd': strncpy(value, "1101", 4); break;
             case 'e': strncpy(value, "1110", 4); break;
             case 'f': strncpy(value, "1111", 4); break;
             default:  printf("Something is wrong here...");
	         }
	         sprintf(buf + strlen(buf), "%s", value);        
        }
    }
    //Skip first four bytes (false, cause: buf + strlen(buf)
    char* binary = buf + 4;
    return binary;
}

HexToBinary.h

#ifndef HexToBinary_h
#define HexToBinary_h

#include <stdint.h>

class HexToBinary
{
  public:
    HexToBinary();
    char* convert(char hexdec[]);
};

#endif