Encryption and Decryption encryption Affine cipher code

Encryption and Decryption encryption Affine cipher code implementation
cpp code

#include<stdio.h>
#include<string.h>
void main()
{
	int ch,a1,b1,a,b,c,d,d1[15],h,n,i=0;
	char str1[80],ek[80];
	printf("Enter the text \n");
	gets(str1);
  	do
	{
	printf("Enter the key \na:");
	scanf("%d",&a);
	printf("\nb:");
	scanf("%d",&b);
	a1=a;
	b1=b;
	b=26;
	d=1;
	while(d!=0)
	{
		
		
			c=a/b;
			
			d=a%b;
			d1[i]=d;
			a=b;
			b=d;
		i=i++;
		
		

	}
	
	n=i-1;

	
	
	

			if(d1[n-1]==1)
			{
				printf("\nOi ariumoi einai prvtoi metaji tous\n\n");
				ch=1;

			}
			else 
			{
				printf("\nOi ariumoi den einai prvtoi metaji tous\n\n");
				ch=0;
			}
	}
	while(ch==0);
			a=a1;
			b=b1;
			printf("\nTo kleidi einai (%d,%d):\n",a,b);

			printf("\nTo keimeno einai %s  to mikos toy %d	\n",str1,strlen(str1));
			n=strlen(str1);
		
			ek[n]='\0';
			h=strlen(ek);
			for (i=0; i<h; i++)
			{
				str1[i]=str1[i]-97;
				ek[i]=((a*str1[i]+b)%26)+97;
				printf("%c -> %d to \n",str1[i]+97,str1[i]);
			}
			
			printf("\n\nTo kriptografhmeno keimeno einai:%s \n",ek);
			for (i=0; i<h; i++)
			{
				printf("%c -> %d \n",ek[i],ek[i]-97);
			}
			printf("To kriptografhmeno keimeno einai:%s \n\n",ek);
			
}

decryption :
cpp code

#include<stdio.h>
#include<string.h>
void mul(int a1,int b1,int *d,int *x,int *y);
void main()
{
	int ch,xx,a1,b1,a,b,c,d,d1[15],h,n,x,key,y,i=0;
	char str1[80],dk[80];
	printf("Enter the text \n");
	gets(str1);
  	do
	{

	printf("Enter the key \na:");
	scanf("%d",&a);
	printf("\nb:");
	scanf("%d",&b);

	a1=a;
	b1=b;
	b=26;
	mul(a,b,&d,&x,&y);
	key=x;
	if (key<0)
	{
		key=26+key;
	}
	printf("\n1/a:%d \n",key);

	d=1;
	while(d!=0)
	{
		
		
			c=a/b;
			
			d=a%b;
			d1[i]=d;
			a=b;
			b=d;
		i=i++;
		
		

	}
	
	n=i-1;

	
	
	

			if(d1[n-1]==1)
			{
				printf("\nOi ariumoi einai prvtoi metaji tous\n\n");
				ch=1;

			}
			else 
			{
				printf("\nOi ariumoi den einai prvtoi metaji tous\n\n");
				ch=0;
			}
	}
	while(ch==0);
			a=a1;
			b=b1;
			printf("\nTo kleidi einai (%d,%d):\n",a,b);

			printf("\nTo keimeno einai %s  to mikos toy %d	\n",str1,strlen(str1));
			n=strlen(str1);
		
			dk[n]='\0';
			h=strlen(dk);
			for (i=0; i<h; i++)
			{
				str1[i]=str1[i]-97;
				xx=(str1[i]-b)%26;/*to kano se periptosi pou o b einai megalos*/
				if (xx<0)
				{
					xx=26+xx;
				}
				
				dk[i]=((key*(xx))%26)+97;
				printf("%c -> %d\n",str1[i]+97,str1[i]);
			}
			printf("\n\nTo kriptografhmeno keimeno einai:%s \n",dk);
			for (i=0; i<h; i++)
			{
				printf("%c -> %d\n",dk[i],dk[i]-97);
			}
			printf("To kriptografhmeno keimeno einai:%s \n\n",dk);
			
}

void mul(int a1,int b1,int *d1,int *x1,int *y1)
{int c,d,x,y;
	if(b1==0)
	{
		*d1=a1;
		*x1=1;
		*y1=0;
		
	
	}
	else{
	d=*d1;
	x=*x1;
	y=*y1;
		


c=a1%b1;

mul(b1,c,&d,&x,&y);
	

*d1=d;
*x1=y;
*y1=x-(a1/b1)*(y);

	}
	
}