| 1 | #include <stdio.h> |
| 2 | #include <stdlib.h> |
| 3 | |
| 4 | int stringLength(const char* str) { |
| 5 | int result = 0; |
| 6 | |
| 7 | for (; str[result]; ++result); |
| 8 | |
| 9 | return result; |
| 10 | } |
| 11 | |
| 12 | void swap(char* v1, char* v2) { |
| 13 | char temp = *v1; |
| 14 | *v1 = *v2; |
| 15 | *v2 = temp; |
| 16 | } |
| 17 | |
| 18 | void reverseString(char* str) { |
| 19 | char* begin = str; |
| 20 | char* end = str + stringLength(str) - 1; |
| 21 | |
| 22 | while (begin < end) { |
| 23 | swap(begin++, end--); |
| 24 | } |
| 25 | } |
| 26 | |
| 27 | /** Perform a classical ROT13 permutation in-place */ |
| 28 | void rot13(char* str) { |
| 29 | char* cursor = str; |
| 30 | char* end = str + stringLength(str); |
| 31 | |
| 32 | while (cursor < end) { |
| 33 | if (*cursor >= 'a' && *cursor <= 'z') { |
| 34 | *cursor = (*cursor - 'a' + 13) % 26 + 'a'; |
| 35 | } else if (*cursor >= 'A' && *cursor <= 'Z') { |
| 36 | *cursor = (*cursor - 'A' + 13) % 26 + 'A'; |
| 37 | } |
| 38 | |
| 39 | ++cursor; |
| 40 | } |
| 41 | } |
| 42 | |
| 43 | int main() { |
| 44 | char* msg; |
| 45 | puts("Enter your message:"); |
| 46 | int readValue = scanf("%ms", &msg); |
| 47 | |
| 48 | if (readValue == 0) { |
| 49 | puts("oops"); |
| 50 | return 0; |
| 51 | } |
| 52 | |
| 53 | printf("Initial value: \"%s\"\n", msg); |
| 54 | reverseString(msg); |
| 55 | printf("Reversed : \"%s\"\n", msg); |
| 56 | reverseString(msg); // Restore the original message |
| 57 | rot13(msg); |
| 58 | printf("ROT13 : \"%s\"\n", msg); |
| 59 | free(msg); // scanf("%ms") allocate dynamic memory |
| 60 | } |