#include "stdio.h"

void main()
{  
	int code_in;
	int i,j,a;
	int code_out[15];
	int mid[15];

/*  code  */
	int g[15]={0x1,0x2,0x4,0x8,0x10,0x20,0x40,0x80,0x100,0x200,0x365,0x1AF,0x35E,0x1D9,0x3B2};

	printf("輸入原始信息數據(16進制):");
	scanf("%x",&code_in);

	for(i=0;i<15;i++)
	{
		a=code_in&g[i];
		for(j=0;j<10;j++)
		{
			mid[j]=a&1;
			a=a>>1;
		}
		code_out[i]=mid[0];
		for(j=1;j<10;j++)
			code_out[i]=code_out[i]^mid[j];
	}

	printf("糾錯編碼后的輸出比特流： ");
	for(i=15;i>0;i--)
		printf("%d",code_out[i-1]);

/* decode and correct */  
	for (i=0;i<15;i++)
	{ 
		code_out[i]=0;
		mid[i]=0;
	}
	code_in=0;
	i=0;
	j=0;
	a=0;
  
	int check_out[5];
	int errorflag,matchbit,matchflag,comparebit;
	int check[5]={0x765,0x9AF,0x135E,0x21D9,0x43B2};  /*the check array*/

	printf("\n輸入接受端收到的原始數據(16進制):");
	scanf("%x",&code_in);    /*input the data received at the receiver*/

	a=code_in;
	for (i=0;i<15;i++)      /*change the data received into bits*/
	{ 
		code_out[i]=a&1;
		a=a>>1;
	}

	for(i=0;i<5;i++)        /*caculate the cheksum*/
	{  
		a=code_in&check[i];
		for(j=0;j<15;j++)    /*get every bit of a */
		{
			mid[j]=a&1;
			a=a>>1;
		}
		check_out[i]=mid[0];
		for(j=1;j<15;j++)
			check_out[i]=check_out[i]^mid[j]; /*add the bits in mode 2*/
	}

	i=0; 
	errorflag=0;
	do 
	{
		if (check_out[i]==1) 
		{ 
			errorflag=1; 
			i=5;
		}
		else 
			i++;
	}
	while (i<5);     /* check if the check is all 0 */

	if (errorflag==1)
	{   
		i=0;  
		matchbit=100;      /* look for the same line*/
		do  
		{ 
			j=0; 
			matchflag=1;
			do 
			{ 
				comparebit=(check[j]>>i)&1; /* get the [j][i] bit of the array*/
	    		if (check_out[j]!=comparebit) 
				{
					j=5;
					matchflag=0;
				}                /*not coincident,jump out at once*/
				else 
					j++;
			} 
			while (j<5);
	       
			if (matchflag==1) 
			{
				matchbit=i;
				i=15;
			}               /*if found,jump out at once*/
			else 
				i++;
		}
		while (i<15);
     
		if (matchbit<=14)
		{
			code_out[matchbit]=code_out[matchbit]^1;    /*correct the error bit*/
			printf("第%d位數據出錯!\n",matchbit+1);
		}
		else 
			printf("錯誤但不可糾!\n");
	}
	else printf("傳輸正確或錯誤不可檢!\n");

	printf("還原的信息比特為:");
	for (i=10;i>0;i--)                     /*only print the information bits*/
		printf("%d",code_out[i-1]);
}