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

void main()
{
	int m;
	int r;
	int db[30];
	
	cout<<"\n Enter frame size:";
	cin>>m;
	
	int i,j,k; //Some temp variables
	
	cout<<"\n Enter Frame :";
	for (i=0;i<m;i++)
	{
		cin>>db[i];
	}

	cout<<"\n Enter redundancy bits: ";
	cin>>r;
	
	//Entered Frame
	cout<<"\n Frame :\n ";
	for(i=0;i<m;i++)
	{
		cout<<db[i]<<" ";
	}

	//Reverse db[] for further processing
	int temp[30];
	for (i=m-1,j=0;i>=0;i--,j++)
	{
		temp[j]=db[i];
	}
	for (i=0;i<m;i++)
	{
		db[i]=temp[i];
	}

	/* Redundancy bits */
	int nrb=0;		// Counter for number of redundancy bit
	int rb[8];		// Array to hold redundancy bits

	/* New Frame after introducing redundancy bits */
	int l=0;		// Length of new frame = l = m+r
	int df[30];		// New frame

	// Introduce redundancy bits and construct new frame
	k=1;
	for(i=1,j=0;j<m;i++)
	{
		//If it is location of redundancy bit
		if(i==k)
		{
			df[i]=-1;
			k=k*2;
			nrb++;
		}
		//If it is location of data bit
		else
		{
			df[i]=db[j];
			j++;
		}
		l++;
	}

	cout<<"\n";
	cout<<"\n Frame after introducing redundancy bits :\n ";
	for(i=l;i>0;i--)
	{
		cout<<df[i]<<" ";
	}

	//Some more temp variables and arrays
	int i1,i2,i3,i4,i5,i6,i7;
	int a1[4],a2[4];
	
	i5=0;		//Holds position of rb[]

	//Scan Whole frame and calculate all redundancy bits
	for(i1=1;i1<=l;i1++)
	{
		//check if it is redundancy bit which is to be calculated
		if(df[i1]==-1)
		{
			//Get the position of 1 from binary representation
			i4 = -1;	//Hold position of 1
			
			//Converting redundancy bit position into binary form and get position of 1
			i7=i1;
			while (i7>0)
			{
				i4++;
				if(i7==1)
				{
					break;
				}
				else
				{
					i7=i7/2;
				}
			}

			i3=0; // Consider even parity

			//Calculating redundancy bit and parity
			for(i2=1;i2<=l;i2++)
			{
				//reset a1 frame
				for(i6=0;i6<4;i6++)
				{
					a1[i6]=-1;
				}

				//find binary conversion for each position
				i7=i2;
				i6=0;
				while(i7>0)
				{
					if(i7==1)
					{
						a1[i6]=1;
						break;
					}
					else if(i7==0)
					{
						a1[i6]=0;
					}
					else
					{
						a1[i6]=i7%2;
						i7=i7/2;
					}
					i6++;
				}

				//check that the binary conversion is having bit at specific position or not
				//if yes calculate parity
				
				if(a1[i4]==1)
				{
					if(df[i2]==1)
					{
						i3++;
					}
				}
				
			}

			//Display Parity
			//Add redundancy bit in data frame
			//odd parity -> 1 :: even parity -> 0

			if(i3%2==0)
			{
				df[i1]=0;
				rb[i5]=0;
			}
			else
			{
				df[i1]=1;
				rb[i5]=1;
			}
			i5++;

			//Print current frame
			cout<<"\n R"<<i5<<" = "<<rb[i5-1]<<"\t New Frame";
			for(i2=l;i2>0;i2--)
			{
				cout<<" "<<df[i2];
			}
		}
	
	}

	//Get the error bit
	int eb;
	cout<<"\n";
	cout<<"\n Enter bit number where error is occurred: ";
	cin>>eb;
	
	cout<<"\n Bit at position "<<eb<<" is "<<df[eb];
	
	//Change bit
	if(df[eb]=1)
	{
		df[eb]=0;
	}
	else
	{
		df[eb]=1;
	}
	
	cout<<" and now changed to "<<df[eb];
	
	// Print new frame after changing the bit
	cout<<"\n New Frame is";
	for(i=l;i>0;i--)
	{
		cout<<" "<<df[i];
	}

	//Recalculate everything

	i5=0;
	k=1;
	//Scan Whole frame
	for(i1=1;i1<=l;i1++)
	{		
		//Do processing only for redundancy bits
		if (i1==k)
		{
			//Get the position of 1 from binary representation
			i4 = -1; //Hold position of 1
		
			//Converting redundancy bit into binary form and get position of 1
			i7=i1;
			while (i7>0)
			{
				i4++;
				if(i7==1)
				{
					break;
				}
				else
				{
					i7=i7/2;
				}
			}

			i3=0; // Consider even parity
		
			//Calculating redundancy bit and parity
			for(i2=1;i2<=l;i2++)
			{
				//reset a1 frame
				for(i6=0;i6<4;i6++)
				{
					a1[i6]=-1;
				}
			
				//find binary conversion
				i7=i2;
				i6=0;
				while(i7>0)
				{
					if(i7==1)
					{
						a1[i6]=1;
						break;
					}
					else if(i7==0)
					{
						a1[i6]=0;
					}
					else
					{
						a1[i6]=i7%2;
						i7=i7/2;
					}
					i6++;
				}
			
				//check that the binary conversion is having bit at specific position or not
				//if yes calculate parity
			
				if(a1[i4]==1)
				{
					if(df[i2]==1)
					{
						i3++;
					}
				}
				
			}

			//Display Parity
			//Add redundancy bit in data frame
			//odd parity -> 1 :: even parity -> 0
		
			if(i3%2==0)
			{
				df[i1]=0;
				rb[i5]=0;
			}
			else
			{
				df[i1]=1;
				rb[i5]=1;
			}
		
			i5++;
		
			k=k*2;
		}

	}

	cout<<"\n Redundancy bits:";
	for(i=0;i<nrb;i++)
	{
		cout<<" "<<rb[i];
	}

	//Calculate error position
	int ep=0;
	for(i=0,j=1;i<nrb;i++)
	{
		if(rb[i]==1)
		{
			ep=ep+j;
		}
		j=j*2;
	}

	cout<<"\n Error is at : "<<ep;

	getch();
}

/* OUTPUT

 Enter frame size:7

 Enter Frame :1
0
0
1
1
0
1

 Enter redundancy bits: 4

 Frame :
 1 0 0 1 1 0 1

 Frame after introducing redundancy bits :
 1 0 0 -1 1 1 0 -1 1 -1 -1
 R1 = 1  New Frame 1 0 0 -1 1 1 0 -1 1 -1 1
 R2 = 0  New Frame 1 0 0 -1 1 1 0 -1 1 0 1
 R3 = 0  New Frame 1 0 0 -1 1 1 0 0 1 0 1
 R4 = 1  New Frame 1 0 0 1 1 1 0 0 1 0 1

 Enter bit number where error is occurred: 7

 Bit at position 7 is 1 and now changed to 0
 New Frame is 1 0 0 1 0 1 0 0 1 0 1
 Redundancy bits: 1 1 1 0
 Error is at : 7

 */