平成20年度秋期試験_基本情報午後問10

h20a_fe_pm10.c

#include <stdio.h>

#define ROWS 4                  /* 換字表の行数 */
#define COLS 23                 /* 換字表の列数 */

void encrypt_text(const char *, const char *,
                  const char[ROWS][COLS]);
void decrypt_text(const char *, const char *,
                  const char[ROWS][COLS]);
void make_ctbl(char [ROWS][COLS]);

void encrypt_text(const char *in_filename,
                  const char *out_filename,
                  const char ctbl[ROWS][COLS]) {
  FILE *ifp, *ofp;
  char ch[2];
  int col[2], row[2], flg, i, sts;
  int cnt2;
  
  ifp = fopen(in_filename, "r");
  ofp = fopen(out_filename, "w");
  do {
    sts = fgetc(ifp);
    while ((char)sts == '\n') {
      fputc('\n', ofp);
      sts = fgetc(ifp);
    }
    if (sts != EOF) {           
      ch[0] = sts;
      cnt2 = 0;
      sts = fgetc(ifp);
      while ((char)sts == '\n') {
        cnt2++;
        sts = fgetc(ifp);
      }
      if (sts == EOF) {         /* 文字列が奇数の場合 */
        ch[1] = ' ';
      } else {
        ch[1] = sts;
      }
      for (i = 0; i < 2; i++) {
        flg = 0;
        for (row[i] = 0; row[i] < ROWS; row[i]++) {
          for (col[i] = 0; col[i] < COLS; col[i]++) {
            if (ch[i] == ctbl[row[i]][col[i]]) {
              flg = 1;
              break;
            }
          }
          if (flg != 0) break;
        }
      }
      if (row[0] == row[1]) {
        if (col[0] == col[1]) { /* 2文字が同一の場合 */
          ch[0] = ch[1] = ctbl[(row[0] + 1) % ROWS][(col[0] + 1) % COLS];
        } else {                /* 2文字が同じ行にある場合 */
          ch[0] = ctbl[row[0]][(col[0] + 1) % COLS];
          ch[1] = ctbl[row[1]][(col[1] + 1) % COLS];
        }
      } else if (col[0] == col[1]) { /* 2文字が同じ列にある場合 */
        ch[0] = ctbl[(row[0] + 1) % ROWS][col[0]];
        ch[1] = ctbl[(row[1] + 1) % ROWS][col[1]];
      } else {
        ch[0] = ctbl[row[0]][col[1]];
        ch[1] = ctbl[row[1]][col[0]];
      }
      fputc(ch[0], ofp);
      for (; cnt2 > 0; cnt2--) {
        fputc('\n', ofp);
      }
      fputc(ch[1], ofp);
    }
  } while (sts != EOF);
  fclose(ifp);
  fclose(ofp);
}

void decrypt_text(const char *in_filename,
                  const char *out_filename,
                  const char ctbl[ROWS][COLS]) {
  FILE *ifp, *ofp;
  char ch[2];
  int col[2], row[2], flg, i, sts;
  int cnt2;
  
  ifp = fopen(in_filename, "r");
  ofp = fopen(out_filename, "w");
  do {
    sts = fgetc(ifp);
    while ((char)sts == '\n') {
      fputc('\n', ofp);
      sts = fgetc(ifp);
    }
    if (sts != EOF) {           
      ch[0] = sts;
      cnt2 = 0;
      sts = fgetc(ifp);
      while ((char)sts == '\n') {
        cnt2++;
        sts = fgetc(ifp);
      }
      ch[1] = sts;
      for (i = 0; i < 2; i++) {
        flg = 0;
        for (row[i] = 0; row[i] < ROWS; row[i]++) {
          for (col[i] = 0; col[i] < COLS; col[i]++) {
            if (ch[i] == ctbl[row[i]][col[i]]) {
              flg = 1;
              break;
            }
          }
          if (flg != 0) break;
        }
      }
      if (row[0] == row[1]) {
        if (col[0] == col[1]) { /* 2文字が同一の場合 */
          ch[0] = ch[1] =
            ctbl[(row[0] + ROWS - 1) % ROWS][(col[0] + COLS - 1) % COLS];
        } else {                /* 2文字が同じ行にある場合 */
          ch[0] = ctbl[row[0]][(col[0] + COLS - 1) % COLS];
          ch[1] = ctbl[row[1]][(col[1] + COLS - 1) % COLS];
        }
      } else if (col[0] == col[1]) { /* 2文字が同じ列にある場合 */
        ch[0] = ctbl[(row[0] + ROWS - 1) % ROWS][col[0]];
        ch[1] = ctbl[(row[1] + ROWS - 1) % ROWS][col[1]];
      } else {
        ch[0] = ctbl[row[0]][col[1]];
        ch[1] = ctbl[row[1]][col[0]];
      }
      fputc(ch[0], ofp);
      for (; cnt2 > 0; cnt2--) {
        fputc('\n', ofp);
      }
      fputc(ch[1], ofp);
    }
  } while (sts != EOF);
  fclose(ifp);
  fclose(ofp);
}

void make_ctbl(char ctbl[ROWS][COLS]) {
  int i, j;
  for (i = 0; i < ROWS; i++) {
    for (j = 0; j < COLS; j++) {
      ctbl[i][j] = i * COLS + j + 0x20;
      printf("%c", ctbl[i][j]);
    }
    printf("\n");
  }
}

int main(int argc, char *argv[]) {
  char ctbl[ROWS][COLS];

  if (argc != 4) {
    printf("Usage: %s e|d file1 file2\n", argv[0]);
    return 1;
  }

  make_ctbl(ctbl);              /* 換字表の作成 */
  switch (*argv[1]) {
  case 'e':
    encrypt_text(argv[2], argv[3], ctbl);
    break;
  case 'd':
    decrypt_text(argv[2], argv[3], ctbl);
    break;
  }
  return 0;
}

平成20年度秋季基本情報午後問10 - Mae向きなブログ