Cranes at VIIT Q2

String Encryption with Shift Cipher

Write a C program that encrypts a given string using a modified shift cipher with specified conditions.

Problem Statement:

• The user provides a string s that may contain:
  • Alphabets (both uppercase and lowercase)
  • Digits (0-9)
  • Special characters (which remain unchanged)
• Apply the following encryption rules:
  • Lowercase Characters: Shift by k positions with wrap-around.
  • Uppercase Characters: Shift by k positions with wrap-around.
  • Digits: Reverse the digit (e.g., 2 becomes 7, 8 becomes 1).
  • Special characters remain unchanged.

Encryption Logic:

• Lowercase: s[i] = (s[i] - 'a' + k) % 26 + 'a'
• Uppercase: s[i] = (s[i] - 'A' + k) % 26 + 'A'
• Digit: Reverse by 9 - (s[i] - '0') + '0'

Input Format:

• s: A string that may contain alphabets, digits, and special characters.
• k: An integer representing the shift value.

Output Format:

• Print the encrypted string after applying the shift cipher.

Example Inputs & Outputs:

Enter the string: Hello123
Enter the shift value: 3
Encrypted string: Khoor876
            

Enter the string: Cipher99!
Enter the shift value: 5
Encrypted string: Hnumjw00!
            

Constraints:

• 1 ≤ length of s ≤ 1000
• 0 ≤ k ≤ 25

Hint:

Follow these steps to solve the problem:

1. Take Input:
   • Read the string s that may contain alphabets, digits, and special characters.
   • Read an integer k representing the shift value.
2. Iterate Through the String:
   • Use a loop to iterate through each character of the string.
   • Check the type of character encountered.
3. Check the Character Type:
   • If the character is a lowercase letter (between 'a' and 'z'):
     • Shift it by k positions with wrap-around.
     • Use the formula:

       s[i] = (s[i] - 'a' + k) % 26 + 'a';

   • If the character is an uppercase letter (between 'A' and 'Z'):
     • Shift it by k positions with wrap-around.
     • Use the formula:

       s[i] = (s[i] - 'A' + k) % 26 + 'A';

   • If the character is a digit (between '0' and '9'):
     • Reverse the digit using:

       s[i] = 9 - (s[i] - '0') + '0';

   • If the character is a special character (not a letter or digit), leave it unchanged.
4. Print the Result:
   • After processing all characters, print the modified string.

Formula Breakdown:

• To shift lowercase letters:

  s[i] = (s[i] - 'a' + k) % 26 + 'a';

• To shift uppercase letters:

  s[i] = (s[i] - 'A' + k) % 26 + 'A';

• To reverse digits:

  s[i] = 9 - (s[i] - '0') + '0';

Task: Implement the above logic and write a C program to encrypt the string.