Program to implement character level encryption by monoalphabetic encryption method.

Write a program to implement character level encryption by monoalphabetic encryption method.

Program Code:

#include
#include
#include
#include
void main()
{
FILE *fp,*ft;
char ch,s[100],x;
char ci[]={'k','c','p','s','v','m','h','f','d','b','u','w','q','n','r','y','t','j','o','i','x','e','l','a','z','g'};
int i;
clrscr();
printf("=========Sender Side============\n\n");
fp=fopen("cipher.txt","w+");
ft=fopen("cipher1.txt","w+");
if(fp==NULL)
{
printf("\nCannot Open File");
getch();
exit(0);
}
printf("\nEnter Few Lines of Text\n\n");
while(strlen(gets(s))>0)
{
fputs(s,fp);
fputs("\n",fp);
}

rewind(fp);
while(1)
{
ch=fgetc(fp);
if(ch==EOF)
break;
else
{
if(ch>=97 && ch<=122)
{
ch=ch-97;
fputc(ci[ch],ft);

}
else if(ch>=65 && ch<=90)
{
ch=ch-65;
fputc(toupper(ci[ch]),ft);
}
else
fputc(ch,ft);
}
}
rewind(ft);
printf("\n\nCipher Text After Monoalphabetic Substitution Is:\n");
printf("-------------------------------------------------\n\n");
while(1)
{
ch=fgetc(ft);
if(ch==EOF)
break;
printf("%c",ch);

}
rewind(fp);
rewind(ft);
printf("\n\n========Receiver Side==========\n\n");
while(1)
{
ch=fgetc(ft);
if(ch==EOF)
break;
else
{
if((ch>=97 && ch<=122) || (ch>=65 && ch<=90))
{
for(i=0;i<26;i++)
{ x=ch;
if(ci[i]==tolower(x))
break;
}
if(isupper(ch))
fputc(65+i,fp);
else
fputc(97+i,fp);
}
else
fputc(ch,fp);
}
}
rewind(fp);
printf("\n\nMessage Sent From Sender Side Is\n");
printf("-------------------------------------------------\n\n");
while(1)
{
ch=fgetc(fp);
if(ch==EOF)
break;
printf("%c",ch);

}
fclose(ft);
fclose(fp);
getch();
}

Output:

=========Sender Side============

Enter Few Lines Of Text

WARNING: it's a virus

Cipher Text After Monoalphabetic Substitution Is:
--------------------------------------------------
LKJNDNH: di'o k edjxo

========Receiver Side==========

Message Sent From Sender Side Is
-------------------------------------------------
WARNING: it's a virus