使用scanf（）读取字符 [英] Reading character with scanf()

问题描述

此代码适用于垃圾游戏。

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

int roll_dice(void);
bool play_game(void);

int main()
{
   int i, ch,win = 0,lose = 0;
   bool flag;
   srand((unsigned)time(NULL));

   do
   {
       flag = play_game();
       if(flag)
       {
           printf("You win!");
           win++;
       }
       else
       {
           printf("You lose!");
           lose++;
       }

       printf("\n\nPlay again(Y/N)? ");
       scanf("%c", &ch);
       ch = getchar();
       printf("\n");
   }while(ch == 'Y' || ch == 'y');

   printf("\nWins: %d   Losses: %d",win,lose);
   return 0;
}

int roll_dice(void)
{
    return rand()%6 + rand()%6 + 2;
}

bool play_game(void)
{
   int sum = roll_dice();

   printf("You rolled: %d\n", sum);
   if(sum == 7 || sum == 11)
       return 1;
   else if(sum == 2 || sum == 3 || sum == 12)
       return 0;    
   else
   {
       int point = sum;
       printf("Your point is: %d\n", point);
       do
       {
           sum = roll_dice();
           printf("You rolled: %d\n", sum);
           if(sum == 7)
               return 0;            
       }while(point != sum);
       return 1;
   }                    
}

我有问题只有代码片段

 printf("\n\nPlay again(Y/N)? ");
 scanf("%c", &ch);
 ch = getchar();
 printf("\n");

我已经使用，因为它在一次迭代后终止，无论用户输入 Y 或 N 。我想我放错了 ch = getchar（）吃了 \\\
在转换说明符之前放置一个空格，并替换为％c这也没有工作。当我替换转换说明符％d 它工作正常。

这是什么问题？

我访问了这个 post ，这是我说的同样的事情。

I have used, because it terminates after one iteration whatever user input Y or N. I thought I am doing wrong by placing ch = getchar() to eat up \n, I removed it and placed a space before conversion specifier and replaced it by " %c" which also did't work.When I replaced the conversion specifier by %d it works fine.
Is anything going wrong with this?
I visited this post and it is saying same thing I did.

推荐答案

发布的代码具有未定义的行为，因为 ch code> int 且格式说明符％c 必须与 char 匹配。

The posted code has undefined behaviour because ch is of type int and the format specifier %c must match a char.

当我替换转换说明符％d时，它工作正常。

When I replaced the conversion specifier %d it works fine.

当您切换到％d Y 或 ，您无法使用 scanf（）不是 int ，因此不会消耗任何输入（除了在循环的后续迭代中丢弃新行字符的前导空白空间）和随后的 ch = getchar（）实际上读取用户输入的字符，并且代码通过fluke工作。始终检查 scanf（）的返回值，它返回已完成的分配数。

When you switch to %d the scanf() fails, because Y or y is not an int, so no input is consumed (apart from leading whitespace which discards the new line character on subsequent iterations of the loop) and the subsequent ch = getchar() actually reads the user entered character, and the code works by fluke. Always check the return value of scanf(), which returns the number of assignments made.

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