Question

The following code is a C Program that is written for encrypting and decrypting a string. provide a full explanation of the working flow of the program.

#include <stdio.h> int main() { int i, x; char str[100]; printf("\n Please enter a valid string: \t"); gets (str); printf ("\n Please choose one of the following options: \n"); printf ("1 = Encrypt the given string. \n"); printf("2 = Decrypt the entered string. \n"); scanf("%d",&x); // using switch case statements switch (x) { case 1: for (i = 0; (i < 100 && str[i] != '\0'); i++) str[i] = str[i] + 3; // the key for encryption is 3 that is added to ASCII code vlaue printf("\n Encrypted string: %s\n", str); break; case 2: for (i = 0; i < 100 && str[i] != '\0'); i++) str[i] = str[i] - 3; //the key for encryption is 3 that is subtracted to ASCII code value printf("\n Decrypted string: %s\n", str); break; default: printf("\n Error in process \n"); } return 0;

Answer 1

EXPLAINATION -

So, in the above code, at first user will enter a string of length upto 100.

After that, we have 2 choices. First, we can encrypt the given string i.e. we will change the original string. And the second option is , we can decrypt the string i.e. we are assuming the given string is itself a changed string and we have to retrieve our original string.

So, when we select the first choice we will change the original string. For that we are traversing the whole string and increasing the ASCII value of the characters by 3. This means if the given string is 'abcdef' , after completing the encryption , it will become 'defghi' which is nothing but out encrypted string.

Now, if we select the second choice, we have to retrieve the original string. For that, again we are traversing the whole string and this time decresing the value of characters by 3. This means if the given string is 'xsyrwh' , after completig the decryption, it will become 'upvote' which is our decrypted string that user want to retrieve.

And, if we select any choice other than these two, we will get the message - "Erorr in proces".