Thread: Encryption and Decryption

I have a school assignment in which asks me to create a program that does the following on encryption and decryption:

Write a program that encrypts and decrypts a text (string). The program reads a text into a character pointer: char * originaltext. Write a function that encrypts originaltext and store the encrypted text into: char * ciphertext. The encryption algorithm is replacing each character by a character having 10 added to its ASCII code. Write another function that decrypts ciphertext and store the result into: char * deciphertext. The decryption algorithm is replacing each character by a character having 10 subtracted from its ASCII code. Display the three strings originaltext, ciphertext,and deciphertext.

It then gives the following hints to start the program:

• Use malloc or calloc functions to allocate dynamically a memory space for strings.
• Assume that the text has a maximum of 100 characters.
• Don’t forget to deallocate the memory using free function.

Could somebody help me to write the program, I'm really stuck and don't know how to start.

So far this is what I have:

Code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>


int main (void) 
{
    char *originaltext;
    char *ciphertext;
    char *deciphertext;
    
    printf("Type In Your String:");
    scanf("%100s",originaltext);
    
    int encryption ();
    {
        *ciphertext = *originaltext + 10;
        return 1;
    };
    
    int decryption ();
    {
        *deciphertext = *ciphertext - 10;
        return 2;
    };

    
    
    if ((originaltext=(char *)malloc(100))==NULL) 
    {
                        printf("Memory allocation error !\n");
                        exit(1);
    }
    
    printf("Original String:\n %s , \nLength of Original String: %i\n",originaltext, strlen(originaltext));
    printf("Encrypted String:\n %s , \nLength of Encrypted String: %i\n",ciphertext, strlen(ciphertext));
    printf("Decrypted String:\n %s , \nLength of Decrypted String: %i\n",deciphertext, strlen(deciphertext));
    free(originaltext);
    
    getchar();
    getchar();
    
    return 0;
}

It's most likely wrong since it gives me a blank window screen

Ok so I modified the program slightly and got it to display the original string I type, but I can't get the encrypt and decrypt functions

Code:

#include <stdio.h>     // Calls for the libraries
#include <string.h>
#include <stdlib.h>

int encrypt (char * originaltext)     // Function to encrypt a string
{
    char * ciphertext;
    
    if (ciphertext)   
    {
        ciphertext = (char *)malloc(100);
         *ciphertext = *originaltext + 10;
         return *originaltext + 10; // Exits encrypt function 
    }
}
    
int decrypt (char * originaltext)     // Function to decrypt a string
{
    char * ciphertext;
    char * deciphertext;
    if (deciphertext)   
    {
         deciphertext = (char *)malloc(100);
         *ciphertext = *originaltext + 10;
         *deciphertext = *ciphertext - 10;
          return *ciphertext - 10; // Exits decrypt function  
    } 
}

int main (void)     // Start of program
{
    char * originaltext;     // Defines pointers
    char * ciphertext; 
    char * deciphertext;
    
    if ((originaltext=(char *)malloc(100))==NULL)   // Sets the maximum number of characters for string
    {
        printf("\nMemory allocation error!\n");
        exit(1);
    }

    printf("Type In Your String:\n\n");        // Asks for the string to be typed
    scanf("%100s",originaltext);               // Allows user to type string
    
    encrypt (originaltext);     // Calls for the encrypt function
    decrypt (originaltext);     // Calls for the decrypt function
    
    printf("\n\nOriginal String:\n\n %s \n\nLength Of Original String: %i",originaltext, strlen(originaltext));     // Displays the original string
    printf("\n\nEncrypted String:\n\n %s \n\nLength Of Encrypted String: %i",ciphertext, strlen(ciphertext));       // Displays the encrypted string
    printf("\n\nDecrypted String:\n\n %s \n\nLength Of Decrypted String: %i",deciphertext, strlen(deciphertext));   // Displays the decrypted string

    free(originaltext);               // Frees the original string
    
    getchar();
    getchar();
    
    return 0;          // End of program
}

I'm using *ciphertext = *originaltext + 10; for encrypt because it's supposed to lead to each character of a string replaced by a character having 10 added, and I'm using *deciphertext = *ciphertext - 10: for decrypt as it's supposed to be the previous *ciphertext subtracted by 10 (I would think that this means *deciphertext points the same as *originaltext)