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April 27, 2016 12:20
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| /** | |
| * vigenere.c | |
| * | |
| * Rafael Beraldo | |
| * rberaldo@cabaladada.org | |
| * | |
| * Encrypts text with the Vigenère cipher | |
| */ | |
| #include <stdio.h> | |
| #include <cs50.h> | |
| #include <stdlib.h> | |
| #include <ctype.h> | |
| #include <string.h> | |
| /* In order for the encryption function to work, we must first get the | |
| alphabetical index of a character by subtracting 65 if it is uppercase and 97 | |
| if it is lowercase. That's because in ASCII, they are not 0-indexed. */ | |
| #define UPPERCASE_ASCII_SHIFT 65 | |
| #define LOWERCASE_ASCII_SHIFT 97 | |
| #define SIZE_ALPHABET 26 | |
| // Functions | |
| void print_usage(string program); | |
| char encrypt(char letter, int key, int shift); | |
| int main(int argc, string argv[]) | |
| { | |
| // Exits if program has less or more than one argument | |
| if (argc != 2) | |
| { | |
| print_usage(argv[0]); | |
| return 1; | |
| } | |
| int key_length = strlen(argv[1]); | |
| char key[key_length]; | |
| /** The case of the key shouldn't change anything, so let's make sure it's | |
| * all lowercase. While we're at that, let's also check there aren't any | |
| * non-alpha characters. | |
| */ | |
| for (int i = 0; i < key_length; i++) | |
| { | |
| if (!isalpha(argv[1][i])) | |
| { | |
| print_usage(argv[0]); | |
| return 1; | |
| } | |
| else | |
| { | |
| key[i] = tolower(argv[1][i]); | |
| } | |
| } | |
| string message = GetString(); | |
| // Cycle though all characters in message | |
| for (int i = 0, j = 0, message_length = strlen(message); i < message_length; i++) | |
| { | |
| // If character isn't alphabetical, we don't need to touch it | |
| if (!isalpha(message[i])) | |
| { | |
| printf("%c", message[i]); | |
| } | |
| // If it is alphabetical, it can be either upper or lowercase | |
| else if (isupper(message[i])) | |
| { | |
| printf("%c", encrypt(message[i], key[j % key_length], UPPERCASE_ASCII_SHIFT)); | |
| j++; | |
| } | |
| else | |
| { | |
| printf("%c", encrypt(message[i], key[j % key_length], LOWERCASE_ASCII_SHIFT)); | |
| j++; | |
| } | |
| } | |
| printf("\n"); | |
| return 0; | |
| } | |
| //////////////////////////////////////////// | |
| /** | |
| * Prints usage information | |
| */ | |
| void print_usage(string program) | |
| { | |
| printf("Usage: %s <keyword>\n", program); | |
| } | |
| /** | |
| * Encrypts a character using a key, shifting to correct for the ASCII table | |
| */ | |
| char encrypt(char letter, int key, int shift) | |
| { | |
| letter -= shift; | |
| return (letter + key - 'a') % SIZE_ALPHABET + shift; | |
| } |
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