Monoalphabetic cipher
#include<stdio.h>
#include<string.h>
int main()
{
char pt[26]={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
char ct[26]={'Z','Y','X','W','V','U','T','S','R','Q','P','O','N','M','L','K','J','I','H','G','F','E','D','C','B','A'};
char p[20]={'\0'},c[20]={'\0'},r[20]={'\0'};
int i,j;
printf("\n Enter the plain text:");
gets(p);
//converting plain text into cipher text (encryption)
for(i=0;i<strlen(p);i++)
{
for(j=0;j<26;j++)
{
if(pt[j]==p[i])
{
c[i]=ct[j];
}
}
}
printf("\n Cipher text is: %s",c);
for(i=0;i<strlen(c);i++)
{
for(j=0;j<26;j++)
{
if(ct[j]==c[i])
{
r[i]=pt[j];
}
}
}
printf("\n \n Plain text is: %s",r);
return 0;
}
OUTPUT
Enter the plain text: COMPUTER
Cipher text is: XLNKFGVI
Plain text is: COMPUTER
