TP_7_C/exo3-full.c

   1 #include <stdio.h>
   2
   3 int stringLength(const char* str) {
   4     int result = 0;
   5
   6     while (str[result] != '\0') {
   7         ++result;
   8     }
   9
  10     return result;
  11 }
  12
  13 void swap(char* v1, char* v2) {
  14     char temp = *v1;
  15     *v1 = *v2;
  16     *v2 = temp;
  17 }
  18
  19 void reverseString(char* str) {
  20     int length = stringLength(str);
  21     int halfLength = length / 2;
  22
  23     for (int charId = 0; charId < halfLength; ++charId) {
  24         swap(&str[charId], &str[length - charId - 1]);
  25     }
  26 }
  27
  28 /** Perform a classical ROT13 permutation in-place */
  29 void rot13(char* str) {
  30     int length = stringLength(str);
  31
  32     for (int charId = 0; charId < length; ++charId) {
  33         char chrValue = str[charId];
  34
  35         if (chrValue >= 'a' && chrValue <= 'z') {
  36             str[charId] =
  37                 (chrValue - 'a' // Translate chrValue from 'a'-'z' to 0-25
  38                  + 13) // Add 13
  39                 % 26 // Rotate in 0-25
  40                 + 'a'; // Translate the value from 0-25 to 'a'-'z'
  41         } else if (chrValue >= 'A' && chrValue <= 'Z') {
  42             str[charId] = (chrValue - 'A' + 13) % 26 + 'A';
  43         }
  44     }
  45 }
  46
  47 int main() {
  48     char msg[] = "Votre message";
  49     printf("Initial value: \"%s\"\n", msg);
  50     reverseString(msg);
  51     printf("Reversed     : \"%s\"\n", msg);
  52     reverseString(msg); // Restore the original message
  53     rot13(msg);
  54     printf("ROT13        : \"%s\"\n", msg);
  55 }