c - 为什么 scanf 对于 char 输入表现得很奇怪？

Question

/* Write macro for the following : 

1. Arithmetic Mean of two no.
2. Absolute value of a no.
3. To convert a Uppercase letter to lower case.
4. To obtain bigger of two numbers.

*/

#include<stdio.h>

#define am(a,b) ((a+b)/2)
#define abs(a) (a>=0?a:-a)
#define ul(ch) (ch>=65 && ch<=96 ? ch+32 : ch)
#define bigger(a,b) (a>=b?a:b)

int main () {

    int x,y;
    char c;

    printf("\nEnter two numbers:");
            scanf("%d%d",&x,&y);

    printf("\nThe arithmetic mean of two numbers is %f",(float)am(x,y));

    printf("\nEnter the number:");
            scanf("%d",&x);

    printf("\nThe absolute value of the number is %d",abs(x));

    printf("\nEnter the character:");
            scanf("%c",&c);

    printf("\nThe letter in lower case  is %c",ul(c));

    printf("\nEnter two numbers:");
            scanf("%d%d",&x,&y);

    printf("\nThe bigger of two numbers is %d",bigger(x,y));


 return 0;

 }

一切正常，只是程序不会因接受字符输入而停止。

这是输出的快照....

  Enter two numbers:4
  5
  The arithmetic mean of two numbers is 4.000000

  Enter the number:-7   **/*After hitting enter here it reaches line no. 7 */** 
  The absolute value of the number is 7

  Enter the character:                                          
  The letter in lower case  is  

  Enter two numbers:4   **/*line no. 7*/**
  6

  The bigger of two numbers is 6

Answer 1

这是因为 %d 跳过了空格，但 %c 没有——换句话说。

%d 将跳过输入流中的任何后续空白，然后输入指针将紧接在最后一位数字之后——这很可能是换行符。因此，当您请求 %c 时，您实际上已经有了输入数据——即您的换行符——这就是您将阅读的内容。

通过在 %c 之前插入一个空格来更改您的 scanf 以要求它跳过空白，所以

   scanf(" %c",&c);