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| #include <cs50.h> | |
| #include <stdio.h> | |
| #include <string.h> | |
| #include <ctype.h> | |
| #include <limits.h> | |
| int main(int argc, string argv[]) | |
| { | |
| if (argc != 2) | |
| { | |
| printf("Usage: ./substitution key\n"); | |
| return 1; | |
| } | |
| string key = argv[1]; | |
| if (strlen(key) != 26) | |
| { | |
| printf("Key must contain 26 characters.\n"); | |
| return 1; | |
| } | |
| // iterate through all key char | |
| for (int i = 0; i < strlen(key); i++) | |
| { | |
| // normalize key as uppercase letters | |
| key[i] = toupper(key[i]); | |
| // special characters are not allowed | |
| bool is_within_a_to_z = key[i] >= 'A' && key[i] <= 'Z'; | |
| if (!is_within_a_to_z) | |
| { | |
| printf("Special characters are not allowed.\n"); | |
| return 1; | |
| } | |
| // duplicated keys are not allowed | |
| for (int j = 0; j < i; j++) | |
| { | |
| // check if any previous key char is the same as current key char | |
| if (key[i] == key[j]) | |
| { | |
| printf("Duplicated keys are not allowed.\n"); | |
| return 1; | |
| } | |
| } | |
| } | |
| string text = get_string("plaintext: "); | |
| for (int i = 0; i < strlen(text); i++) | |
| { | |
| // substitute only alphabets | |
| if ((text[i] >= 'a' && text[i] <= 'z') || (text[i] >= 'A' && text[i] <= 'Z')) | |
| { | |
| // normalize it to upper | |
| char normalized = toupper(text[i]); | |
| // upper case starts at 'A' so 'A'-'A' = 0, 'B'-'A' = 1 and so on | |
| char cipher_char = key[normalized - 'A']; | |
| // check if plaintext char is lowercase, if so, map cipher char to lowercase | |
| if (islower(text[i])) | |
| { | |
| cipher_char = tolower(cipher_char); | |
| } | |
| // update text[i] as cipher char | |
| text[i] = cipher_char; | |
| } | |
| } | |
| printf("ciphertext: %s\n", text); | |
| return 0; | |
| } |
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