http://kin.naver.com/qna/detail.nhn?d1id=1&dirId=1040101&docId=288896228
# include <stdio.h>
# include <string.h>
# include <Windows.h>
//___________________________________________
// 구조체
typedef struct Displacement_cipher {
int k; // secret key
char plainText[50];
char cipherText[50];
char decryptText[50];
}Displacement_cipher, *ptr_dis_cipher;
//___________________________________________
// 함수 원형
ptr_dis_cipher createNode();
void plainText_Write(Displacement_cipher** param);
void secretKey_input(Displacement_cipher** param);
void encrypt_text(Displacement_cipher** param);
void decrypt_text(Displacement_cipher** param);
//___________________________________________
int main(void) {
ptr_dis_cipher node = NULL;
node = createNode();
plainText_Write(&node);
secretKey_input(&node);
encrypt_text(&node);
decrypt_text(&node);
free(node); // 동적 할당 해제
return 0;
} // end of main function
ptr_dis_cipher createNode() { // function _1
ptr_dis_cipher node = (ptr_dis_cipher)malloc(sizeof(Displacement_cipher));
if (node == NULL) { ExitProcess(1); }
else {
// node != NULL
memset(node, 0, sizeof(Displacement_cipher));
return node;
}
} // end of createNode function
void plainText_Write(Displacement_cipher** param) { // function _2
printf("plainText write : ");
fgets((** param).plainText, 50, stdin);
(** param).plainText[strlen((** param).plainText) - 1] = '\0';
system("cls");
printf("PlainText is => [%s]\n", (** param).plainText);
} // end of plainText_Write function
void secretKey_input(Displacement_cipher** param) { // function _3
printf("K value Input (Plz : 0 ~ 25): ");
scanf("%d", &(** param).k);
(** param).k = (** param).k % 26;
system("cls");
printf("SecretKey is => [%d]\n", (** param).k);
} // end of secretKey_input function
void encrypt_text(Displacement_cipher** param) { // function _4
unsigned int i; // index
int j = 0;
int t_enc_indx = 0;
for (i = 0; i < strlen((** param).plainText); i++) {
// 만일 대문자라면
if ((int)(** param).plainText[i] >= 0x41 && (int)(** param).plainText[i] <= 0x5A) {
t_enc_indx = (int)(** param).plainText[i] - 0x41;
t_enc_indx = (t_enc_indx + (** param).k) % 26;
t_enc_indx += 0x41;
(** param).cipherText[j++] = (char)t_enc_indx;
}
// 만일 소문자라면
else if ((int)(** param).plainText[i] >= 0x61 && (int)(** param).plainText[i] <= 0x7A) {
t_enc_indx = (int)(** param).plainText[i] - 0x61;
t_enc_indx = (t_enc_indx + (** param).k) % 26;
t_enc_indx += 0x61;
(** param).cipherText[j++] = (char)t_enc_indx;
}
// 그 어디에도 속해있지 않다면
else {
(** param).cipherText[j++] = (** param).plainText[i];
}
}
(** param).cipherText[j] = '\0';
printf("cipherText is [%s]\n", (** param).cipherText);
} // end of encrypt_text function
void decrypt_text(Displacement_cipher** param) { // function _5
unsigned int i; // index
int j = 0;
int t_dec_indx = 0;
for (i = 0; i < strlen((** param).cipherText); i++) {
// 만일 대문자라면
if ((int)(** param).cipherText[i] >= 0x41 && (int)(** param).cipherText[i] <= 0x5A) {
t_dec_indx = (int)(** param).cipherText[i] - 0x41;
t_dec_indx = (t_dec_indx - (** param).k);
if (t_dec_indx < 0) { t_dec_indx += 26; }
t_dec_indx += 0x41;
(** param).decryptText[j++] = (char)t_dec_indx;
}
// 만일 소문자라면
else if ((int)(** param).cipherText[i] >= 0x61 && (int)(** param).cipherText[i] <= 0x7A) {
t_dec_indx = (int)(** param).cipherText[i] - 0x61;
t_dec_indx = (t_dec_indx - (** param).k);
if (t_dec_indx < 0) { t_dec_indx += 26; }
t_dec_indx += 0x61;
(** param).decryptText[j++] = (char)t_dec_indx;
}
// 그 어디에도 속해있지 않다면
else {
(** param).decryptText[j++] = (** param).cipherText[i];
}
}
(** param).decryptText[j] = '\0';
printf("decryptText is => [%s]\n", (** param).decryptText);
} // end of decrypt_text function
