Question

C Programming Language Please

Given a string S and keyword string K, encrypt S using keyword Cipher algorithm.

Note: The encryption only works on alphabets. Numbers and symbols such as 1 to 9, -, &, $ etc remain unencrypted.

Input:

    Zombie Here

    secret

    where:

• First line represents the unencrypted string S.
• Second line represents the keyword string K.

Output:

    ZLJEFT DTOT

Explanation: We used "secret" keyword there.

• Plain Text: 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, When "secret" keyword is used, the new encrypted text becomes
• Encrypting: S E C R T A B D F G H I J K L M N O P Q U V W X Y Z This means 'A' means 'S', 'B' means 'E' and 'C' means 'C' and so on.

Answer 1

Here I am solving above encryption problem in C language.see below.

encrypted_string.c

#include<stdio.h>
#include<string.h>
int main(){
   char msg[10000],key[100];
   printf("Enter message: ");      // taking input message for encryption
   gets(msg);
   printf("Enter keyword: ");         // taking key as input here
   gets(key);
   strupr(key);                   // converting to upper case
   strupr(msg);                   // both msg and key
   char alphabet[26];
   int ind=0,i;
   for(i=65;i<91;i++)
   {                           // taking alphabets in UPPER case
       char c=i;
       alphabet[i-65]=c;  
   }
   char encrypted[10000];   
   strcpy(encrypted,key);
   strcat(encrypted,alphabet); // merging alphabets and encrypted key
   //printf("%s",encrypted);
   int k=0,j;
   // converting to encrypted one by removing duplicates in string
   char c='*';
   for(i=0;encrypted[i];i++)
    {
       if(!(encrypted[i]==c))
       {
           for(j=i+1;encrypted[j];j++)
            {
               if(encrypted[i]==encrypted[j])
                   encrypted[j]=c;
          
            }  
       }
    }

    for(i=0;encrypted[i];i++)
    {
        encrypted[i]=encrypted[i+k];

        if(encrypted[i]==c)
        {
          k++;
          i--;
        }
       
    }

   // printing resultant encrypted string.   
   for(i=0;i<strlen(msg);i++)
   {
       if(isalpha(msg[i])) // checking only alphabets
       {
           int index=(msg[i])-65;
           printf("%c",encrypted[index]);   // printing each character
       }
       else
           printf("%c",msg[i]);  
   }
      
   return 0;
}

Code - Images:-

output:-

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