C - 使用 while 和 switch/case 的菜单程序返回无效选择的重复菜单

Question

头文件：

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

    int print_menu(){
      printf ("MENU\n");
      printf ("1. Total of All Top Scores for the Week\n");
      printf ("2. Total of All High Scores for the Week\n");
      printf ("3. Total Machine High Scores for the Week\n");
      printf ("4. Machine High Score for the Week\n");
      printf ("5. EXIT\n");
      printf ("Enter Selection:");

      int selection = getchar();
      return selection;
    }

主 C 文件：

    #include <stdio.h>
    #include <stdlib.h>
    #include "lab1.h"

    int main(int argc, char *argv[]){
      int selection = print_menu();
      while(1)
      {
        switch (selection)
        {
          case '1':
            printf ("\nselected 1\n");
            break;
          case '2':
            printf ("\nselected 2\n");
            break;
          case '3':
            printf ("\nselected 3\n");
            break;
          case '4':
            printf ("\nselected 4\n");
            break;
          case '5':
            printf ("\nExit\n");
            exit(0);
            break;
          default:
            printf ("Invalid Selection");
            print_menu();
            break;
        };
      };
    }

我的问题是，当我运行程序并输入错误的字符时，程序应该重新打印菜单并再次要求选择。除了它两次打印菜单。示例：

    maiah@maiah-vb:~/shared$ ./a.out
    MENU
    1. Total of All Top Scores for the Week
    2. Total of All High Scores for the Week
    3. Total Machine High Scores for the Week
    4. Machine High Score for the Week
    5. EXIT
    Enter Selection:d
    Invalid Selection
    MENU
    1. Total of All Top Scores for the Week
    2. Total of All High Scores for the Week
    3. Total Machine High Scores for the Week
    4. Machine High Score for the Week
    5. EXIT
    Enter Selection:
    Invalid Selection
    MENU
    1. Total of All Top Scores for the Week
    2. Total of All High Scores for the Week
    3. Total Machine High Scores for the Week
    4. Machine High Score for the Week
    5. EXIT
    Enter Selection:

然后您可以选择输入另一个选项。 当我通过时，我注意到它似乎正在选择“d”并正确输出，但随后自动输入空格或新行并继续检查选择（我不确定这是否是但实际问题 - 这就是它的表现方式）。如果有人对如何解决此问题有任何想法并解释为什么会发生这种情况。任何帮助都会很棒！

Answer 1

您需要保留打印功能返回的内容。

      default:
        printf ("Invalid Selection");
        selection = print_menu();
        break;

第二个问题是您的 getchar() 调用也会在您选择后返回。添加另一个getchar() 以使用它。

int selection = getchar();
(void) getchar(); /* ignore enter key */
return selection;

附带说明，不要将代码放入标头中，仅放入声明中。
否则，代码将在包含标题的每个代码文件（几个）中编译，并为您带来多个定义错误。如果您只有一个包含标头的代码文件，这并不明显，但您应该尽早养成正确的习惯。

最后你需要经常重新读入，不仅仅是在 5 的情况下。

      default:
        printf ("Invalid Selection");
        break;
    };
    selection = print_menu();
}; /* end of while */

即在循环内但在 case 语句之外执行它，因为只有在没有执行其他任何一个时才会采用默认分支。

Answer 2

试试

  while(1)
  {

      int selection = print_menu();
      switch (selection)
      ....
  }

Answer 3

getchar() 具有从输入缓冲区中删除下一个字符的副作用。

由于scanf() 被告知读取一个且仅一个字符(%c)，这具有忽略该输入行上的所有其他内容的效果。

在重新打印菜单之前也要清除控制台。

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

   int print_menu()
   {
    char selection;

    printf("MENU\n");
    printf("1. Total of All Top Scores for the Week\n");
    printf("2. Total of All High Scores for the Week\n");
    printf("3. Total Machine High Scores for the Week\n");
    printf("4. Machine High Score for the Week\n");
    printf("5. EXIT\n");
    printf("Enter Selection:");

    scanf("%c", &selection);

    return selection;
   }

   int main(int argc, char *argv[])
   {
    int selection;

    while(1) {
      selection = print_menu();

      switch (selection)
      {
        case '1':
          printf("\nselected 1\n");
          exit(selection);
          break;
        case '2':
          printf("\nselected 2\n");
          exit(selection);
          break;
        case '3':
          printf("\nselected 3\n");
          exit(selection);
          break;
        case '4':
          printf("\nselected 4\n");
          exit(selection);
          break;
        case '5':
          printf ("\nExit\n");
          exit(0);
          break;
        default:
          system("@cls||clear");
          printf("\nInvalid Selection\n");
          break;
      };
    };
   }