c - 用于在 switch 语句之前刷新数据的双 while 循环

Question

我需要编写一个脚本，让用户输入 0 到 10 之间的分数，清除错误的输入，如果用户输入它，然后使用 switch 语句，告诉用户他/她得到了什么分数。

这是我的脚本:

         ...
int main()
{
int input;            // input from user

printf("Enter the number between 0 and 10 and I will tell you your grade!");

while ((input=scanf("Your input:", &input) != EOF))
{
    if (input < 0 || input > 10) //input is invalid
    {   
        printf("Sorry, invalid character data.");

        while (getchar() !='\n')
        {   
            printf("Your input must be from 0 to 10.", input);
            scanf("%d", &input); //This part looks very bad for me
        }
    }

    else
        switch (input)
        {                       
            case 0:
            case 1:
            case 2:
            case 3:
            case 4:
            case 5:
                printf("Your grade is F. \n");
                break;  
            case 6:
                printf("Your grade is D. \n");
                break;
          ...

我的作业已经完成了这么多，这里有一些我无法解决的“遗留”问题。

1) 每当用户在输入后提交任何内容时，它都会进入无限循环并打印 Your Grade is F.，即使 case = 6 时也是如此。

2)我在每个案例的末尾使用了break;。看起来它们不起作用(？)

3)看起来问题出在第二个循环的第二行

scanf("%d", &input); //This part looks very bad for me

但我猜脚本会接受它为 true，因为包含 switch 的 else 语句开始起作用，否则它不会打印 Your Grade is F.

Answer 1

尝试以下代码。看看当我们有无效数据时 flush_stream 正在做什么...

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

void flush_stream();

void flush_stream() {
  char c;
  do {
    c = getchar();
  }
  while (!isdigit(c) && c != '\n');
  ungetc(c, stdin);
}

int main(void) {
  const char *prompt = "Input please: ";
  int input;            // input from user
  printf("Enter the number between 0 and 10 and I will tell you your grade!\n");
  while(1) {
    printf("%s", prompt);
    int ret = scanf("%d", &input);
    if(ret == 0) {
      printf("Sorry, invalid character data, your input must be from 0 to 10.\n");
      flush_stream();
      continue;
    }   
    if(ret > 0) {
      if (input < 0 || input > 10) {   
        printf("Sorry, invalid character data, your input must be from 0 to 10.\n");
        flush_stream();
        continue;
      }   

      switch (input) {                            
        case 0:
        case 1:
        case 2:
        case 3:
        case 4:
        case 5:
          printf("Your grade is F. \n");
          break;  
        case 6:
          printf("Your grade is D. \n");
          break;
      }   
    }   
  }
}