cin>>Dan;

char Dan[20];

char *Dan; // Aqui tambien necestias inicializar el apuntador a un tamaño adecuado

string Dan;

#include<stdio.h>
 
unsigned short CRC(unsigned char *s, int len, unsigned short crcval);
 
int main()	{
	unsigned char *test = "\x01\x55\x00\x00";
	printf("CRC: %u\n",CRC(test,4,0));
	return 0;
}
 
unsigned short CRC(unsigned char *s, int len, unsigned short crcval)	{
	register unsigned c,q;
	for (; len; len--)	{
		c = *s++;
		q = (crcval ^ c) & 017;
		crcval = (crcval >> 4) ^ (q * 010201);
		q = (crcval ^ (c >> 4)) & 017;
		crcval = (crcval >> 4) ^ (q * 010201);
	}
	return (crcval);
}

#include<stdio.h>
 
unsigned short CRC(unsigned char *s, int len, unsigned short crcval);
 
int main()	{
	unsigned char *test = "\x01\x55\x00\x00";
	printf("CRC: %u\n",CRC(test,4,0));
	return 0;
}
 
unsigned short CRC(unsigned char *s, int len, unsigned short crcval)	{
	register unsigned c,q;
	printf("Depurando CRC\n");
	for (; len; len--)	{
		printf("len: %i\n",len);
		c = *s++;
		printf("c: %u\n",c);
		q = (crcval ^ c) & 017;
		printf("q: %u\n",q);
		crcval = (crcval >> 4) ^ (q * 010201);
		printf("crcval: %u\n",crcval);
		q = (crcval ^ (c >> 4)) & 017;
		printf("q: %u\n",q);
		crcval = (crcval >> 4) ^ (q * 010201);
		printf("crcval: %u\n",crcval);
	}
	return (crcval);
 

Depurando CRC
len: 4
c: 1
q: 1
crcval: 4225
q: 1
crcval: 4489
len: 3
c: 85
q: 12
crcval: 50964
q: 1
crcval: 7408
len: 2
c: 0
q: 0
crcval: 463
q: 15
crcval: 63379
len: 1
c: 0
q: 3
crcval: 16122
q: 10
crcval: 42725
CRC: 42725

		static void Main(string[] args)
		{
			byte[] test = new byte[] { 0x01,0x55,0x00,0x00 };
			Console.WriteLine("CRC: "+CRC(test,test.Length,0));
		}
 
		public static ushort CRC(byte[] s,int len,ushort crcval) {
			ulong c, q;
			uint i = 0;
			while(len > 0)
			{
				Console.WriteLine("len: "+len);
				c = s[i];
				Console.WriteLine("c: " + c);
				q = (crcval ^ c) & 017;
				Console.WriteLine("q: " + q);
				crcval = (ushort)(((uint)crcval >> 4) ^ (q * 010201));
				Console.WriteLine("crcval: " + crcval);
				q = (crcval ^ (c >> 4)) & 017;
				Console.WriteLine("q: " + q);
				crcval = (ushort)(((uint)crcval >> 4) ^ (q * 010201));
				Console.WriteLine("crcval: " + crcval);
				len--;
				i++;
			}
			return crcval;
		}
 
 

len: 4
c: 1
q: 1
crcval: 10201
q: 17
crcval: 42772
len: 3
c: 85
q: 1
crcval: 11688
q: 1
crcval: 9475
len: 2
c: 0
q: 1
crcval: 9609
q: 1
crcval: 9601
len: 1
c: 0
q: 1
crcval: 9601
q: 1
crcval: 9601
9601