//Ceaser cipher program in c
#include<stdio.h>
#include<string.h>
#include<conio.h>
#include<ctype.h>
void main()
{
int
i,k,b,p,d,dk;
char
in[10],encrpt[10];
clrscr();
printf("\nenter
the plain text:");
gets(in);
printf("\nenter
the key for encrption:");
scanf("%d",&k);
printf("\nencrypted
text:");
for(i=0;i<(strlen(in));i++)
{
if(isupper(in[i]))
{
p=in[i];
p=p+k;
if(p<65)
{
b=65-p;
p=91-b;
}
else
if(p>90)
{
b=p-90;
p=b+64;
}
}
if(islower(in[i]))
{
p=in[i];
p=p+k;
if(p<97)
{
b=97-p;
p=123-b;
}
else
if(p>122)
{
b=p-122;
p=b+96;
}
}
encrpt[i]=p;
printf("%c",p);
}
printf("\nenter
the key for decrption: ");
scanf("%d",&dk);
if(k==dk)
{
printf("\nkey
is correct");
printf("\ndecrepted
text:");
for(i=0;i<(strlen(in));i++)
{
if(isupper(encrpt[i]))
{
d=encrpt[i];
d=d-k;
if(d<65)
{
b=65-d;
d=91-b;
}
else
if(d>90)
{
b=d-90;
d=b+64;
}
}
if(islower(encrpt[i]))
{
d=encrpt[i];
d=d-k;
if(d<97)
{
b=97-d;
d=123-b;
}
else
if(d>122)
{
b=d-122;
d=b+96;
}
}
printf("%c",d);
}
}
else
{
printf("\nenter
valid key");
}
getch();
}
