Implementation of Cyclic Redundancy Check Algorithm in C++

#include <iostream.h>
#include <conio.h>

void main()
{
	int i,j,k,l;
	
	//Get Frame
	int fs;
	cout<<"\n Enter Frame size: ";
	cin>>fs;
	
	int f[20];
	
	cout<<"\n Enter Frame:";
	for(i=0;i<fs;i++)
	{
		cin>>f[i];
	}

	//Get Generator
	int gs;
	cout<<"\n Enter Generator size: ";
	cin>>gs;
	
	int g[20];
	
	cout<<"\n Enter Generator:";
	for(i=0;i<gs;i++)
	{
		cin>>g[i];
	}

	cout<<"\n Sender Side:";
	cout<<"\n Frame: ";
	for(i=0;i<fs;i++)
	{
		cout<<f[i];
	}
	cout<<"\n Generator :";
	for(i=0;i<gs;i++)
	{
		cout<<g[i];
	}

	//Append 0's
	int rs=gs-1;
	cout<<"\n Number of 0's to be appended: "<<rs;
	for (i=fs;i<fs+rs;i++)
	{
		f[i]=0;
	}

	int temp[20];
	for(i=0;i<20;i++)
	{
		temp[i]=f[i];
	}

	cout<<"\n Message after appending 0's :";
	for(i=0; i<fs+rs;i++)
	{
		cout<<temp[i];
	}

	//Division
	for(i=0;i<fs;i++)
	{
		j=0;
		k=i;
		//check whether it is divisible or not
		if (temp[k]>=g[j])
		{
			for(j=0,k=i;j<gs;j++,k++)
			{
				if((temp[k]==1 && g[j]==1) || (temp[k]==0 && g[j]==0))
				{
					temp[k]=0;
				}
				else
				{
					temp[k]=1;
				}
			}
		}
	}

	//CRC
	int crc[15];
	for(i=0,j=fs;i<rs;i++,j++)
	{
		crc[i]=temp[j];
	}

	cout<<"\n CRC bits: ";
	for(i=0;i<rs;i++)
	{
		cout<<crc[i];
	}

	cout<<"\n Transmitted Frame: ";
	int tf[15];
	for(i=0;i<fs;i++)
	{
		tf[i]=f[i];
	}
	for(i=fs,j=0;i<fs+rs;i++,j++)
	{
		tf[i]=crc[j];
	}
	for(i=0;i<fs+rs;i++)
	{
		cout<<tf[i];
	}

	cout<<"\n Receiver side : ";
	cout<<"\n Received Frame: ";
	for(i=0;i<fs+rs;i++)
	{
		cout<<tf[i];
	}

	for(i=0;i<fs+rs;i++)
	{
		temp[i]=tf[i];
	}

	//Division
	for(i=0;i<fs+rs;i++)
	{
		j=0;
		k=i;
		if (temp[k]>=g[j])
		{
			for(j=0,k=i;j<gs;j++,k++)
			{
				if((temp[k]==1 && g[j]==1) || (temp[k]==0 && g[j]==0))
				{
					temp[k]=0;
				}
				else
				{
					temp[k]=1;
				}
			}
		}
	}

	cout<<"\n Reaminder: ";
	int rrem[15];
	for (i=fs,j=0;i<fs+rs;i++,j++)
	{
		rrem[j]= temp[i];
	}
	for(i=0;i<rs;i++)
	{
		cout<<rrem[i];
	}

	int flag=0;
	for(i=0;i<rs;i++)
	{
		if(rrem[i]!=0)
		{
			flag=1;
		}
	}

	if(flag==0)
	{
		cout<<"\n Since Remainder Is 0 Hence Message Transmitted From Sender To Receriver Is Correct";
	}
	else
	{
		cout<<"\n Since Remainder Is Not 0 Hence Message Transmitted From Sender To Receriver Contains Error";
	}
	getch();
}

/* OUTPUT


 Enter Frame size: 6

 Enter Frame:1
0
0
1
0
0

 Enter Generator size: 4

 Enter Generator:1
1
0
1

 Sender Side:
 Frame: 100100
 Generator :1101
 Number of 0's to be appended: 3
 Message after appending 0's :100100000
 CRC bits: 001
 Transmitted Frame: 100100001
 Receiver side :
 Received Frame: 100100001
 Reaminder: 000
 Since Remainder Is 0 Hence Message Transmitted From Sender To Receriver Is Corr
ect

*/

One thought on “Implementation of Cyclic Redundancy Check Algorithm in C++”

  1. There is a mistake in the code. In the receiver side program, while dividing the received message by the generator the for loop i limit should be fs only. Otherwise the crc bits will also be divided by the generator even though they are smaller in size when compared to the generator. So it produces a wrong result.

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