用 C 语言编写一个字母表，显示前面和后面的字母

Question

所以我需要在 C 中发生这种情况，考虑了一个小时左右，但不知道该怎么做，或者如何向谷歌询问这个特定的东西，它必须与输入的任何字母一起工作。

如何计算给定字母的字母表中的下一个和上一个字母？

这是一个链接: http://imgur.com/bRdLonZ

Answer 1

虽然 Dac Saunders 已经给出了很好的解释和一个很好的草图，但我认为有第二个稍微不同的示例也可能会有所帮助。

// for printf() and puts()
#include <stdio.h>
// for exit() and the macro EXIT_SUCCESS
#include <stdlib.h>
// for tolower() and isupper()
#include <ctype.h>

// All calculations assume ASCII encoding!

int main()
{
  char letter;

  puts("Alphabet Facts!");
  puts("^^^^^^^^^^^^^^^");

  // You want an upper case letter as the input, so check for it
  do {
    printf("\nPlease input an uppercase letter: ");
    letter = getc(stdin);
    // swallow new-line(s)
    getc(stdin);
#ifdef _WIN32
    getc(stdin);
#endif
  } while (!isupper(letter));

  printf("\nSome interesting facts:\n\n");

  printf("  1) The lowercase version of the letter is '%c'.\n\n", tolower(letter));
  if (letter == 'A') {
    // or print 'Z' if you want it to mimic a circle
    printf("  2) No letter comes before '%c' in the alphabet.\n", letter);
  } else {
    printf("  2) The letter '%c' comes before '%c' in the alphabet.\n\n", letter - 1, letter);
  }
  if (letter == 'Z') {
    // or print 'A' if you want it to mimic a circle
    printf("  3) No letter comes after '%c' in the alphabet.\n\n", letter);
  } else {
    printf("  3) The letter '%c' comes after '%c' in the alphabet.\n\n", letter + 1, letter);
  }
  // 'A' is at position 64 in the table of the ASCII encoding but we don't need to
  // look it up, we can use the letter itself because a 'char' is a number, too.
  // The ASCII table is zero based--we need to subtract unity from 'A' or add unity
  // after the subtraction of 'A'.
  printf("  4) %c is letter number %d in the alphabet!\n\n", letter, letter - ('A' - 1));
  // return the special number to the OS that tells it that no error occured.
  exit(EXIT_SUCCESS);
}