Cyclic redundancy check Implementation in C

Definition:

A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data found  W. Wesley Peterson in 1961.

CRC working principle:

Blocks of data entering these systems get a short check value attached, based on the remainder of a polynomial division of their contents; on retrieval the calculation is repeated, and corrective action can be taken against presumed data corruption if the check values do not match.

Implementation in C:

/*
* CRC implementation
*
* Author : Rajesh Hegde
*
* Language : C
*
* compiler : gcc
*
*/

#include <stdio.h>
#include <stdlib.h>
int main()
{
	int i, j,k = 0;
	int flag = 1, a[16], g[16], r[20],div[16], n, m;
	system("clear");
	printf("Enter the degree of generator : ");
	scanf("%d", &n);
	printf("\nEnter the generator : \n");
	for(i= 0; i<=n; i++)
		scanf("%d", &g[i]);
	printf("\nEnter the degree of frame : ");
	scanf("%d", &m);
	printf("Enter the frame : \n");
	for(i = 0; i<=m; i++)
		scanf("%d", &a[i]);
 
	if(m<n || (g[0] && g[n]) == 0)
	{
		printf("Not a proper generator \n");
		exit(0);
	}
	for(i = m+1; i<=m+n; i++)
		a[i] = 0;
	for(j= 0; j<=n; j++)
		r[j] = a[j];
	for(i= n; i<=m+n;i++)
	{
		if(i>n)
		{
			for(j = 0; j<n; j++)
				r[j] = r[j+1];
			r[j] = a[i];
		}
		if(r[0])
			div[k++] = 1;
		else
		{
			div[k++] = 0;
			continue;
		}
		for(j= 0; j<=n; j++)
			r[j] = r[j] ^ g[j] ;

	}
	printf("\nQuotient is : ");
	for(j= 0; j<k; j++)
		printf("%d ", div[j]);
	printf("\nReminder is : ");
	for(i= 1; i<=n; i++)
      printf("%d ", r[i]);
	printf("\nTransmitted frame  is : ");
      for(i = m+1,j= 1; i<=m+n;i++, j++)
			a[i] = r[j];
	for(i= 0; i<=m+n; i++)
      printf("%d ", a[i]);
	printf("\n");
		
	printf("\nEnter the degree of frame : ");
   scanf("%d", &m);
   printf("Enter the frame : \n");
   for(i = 0; i<=m; i++)
      scanf("%d", &a[i]);
	for(j = 0; j<=n; j++)
		r[j] = a[j];
	k = 0;
	
	for(i= n; i<=m;i++)
   {
      if(i>n)
      {
         for(j = 0; j<n; j++)
					r[j] = r[j+1];
            r[j] = a[i];
      }
      if(r[0])
         div[k++] = 1;
      else
      {
         div[k++] = 0;
            continue;
      }
      for(j= 0; j<=n; j++)
         r[j] = r[j] ^ g[j] ;
   }
	printf("\nQuotient is : ");
   for(j= 0; j<k; j++)
		printf("%d ", div[j]);
   printf("\nReminder is : ");
   for(i= 1; i<=n; i++)
      printf("%d ", r[i]); 
	for(i= 1; i<=n; i++)
	{
		if(r[i])
			flag = 0;
	} 

	if(flag)
		printf("\n No Error\n");
	else
		printf("\nError");
	return 0;

}