caesar.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

typedef char* string;

string encrypt(int offset, string text);
string decrypt(int offset, string text);
bool gueltige_variablen(string variable);
void help();

int main(int argc, char* argv[])
{
  if (argc  < 4 || !gueltige_variablen(argv[1])) {
    help();
    return 1;
  }
  string text;
  for (int i = 3; i < argc; ++i)
  {
    if (strcmp(argv[1], "-e") == 0)
      text = encrypt(atoi(argv[2]), argv[i]);
    else if (strcmp(argv[1], "-d") == 0)
      text = decrypt(atoi(argv[2]), argv[i]);
    //else if (strcmp(argv[1], "help") == 0);
    //  help();
    printf("%s ", text);
    free(text);
  }
  putchar('\n');
}

string decrypt(int offset, string text)
{
  return encrypt(offset * (-1), text);
}

string encrypt(int offset, string text)
{
  int text_len = strlen(text);
  string encrypted_text = malloc(sizeof(char) * text_len + 1);
  strcpy(encrypted_text, text);

  for (int i = 0; i < text_len; ++i)
  {
    int tmp = (int) encrypted_text[i];
    if (tmp >= 65 && tmp <= 90) //UPPERCASE
      encrypted_text[i] = (char)((tmp - 65 + offset + 26) % 26 + 65);
    else if (tmp >= 97 && tmp <= 122) //lowercase
      encrypted_text[i] = (char)((tmp - 97 + offset + 26) % 26 + 97);
  }
  encrypted_text[text_len] = '\0';
  return encrypted_text;
}

void help() {
  printf("%s\n", "Help:\n\nSyntax: 'caesar -d|-e [offset] [string]'");
}

bool gueltige_variablen(string variable) {
  string variablen[2] = {"-e", "-d"}; // Arraylänge = Anzahl der Variablen + 1
  int variablen_laenge = sizeof(variablen) / sizeof(variablen[0]);
  int ret = false;
  for (int i = 0; i < variablen_laenge ; i++)
  {
    if (strcmp(variablen[i], variable) == 0) {
      ret = true;
      printf("%d\n",(int) ret);
      return ret;
    }
  }
  printf("%d\n",(int) ret );
  return ret;
}