为什么程序的控制流程没有按顺序进行

Question

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

#define DEVICE "/dev/ISMTestDevice"

int main()
{
        int i, fd;
        char ch, wbuf[100], rbuf[100];

        fd = open(DEVICE, O_RDWR);

        if(fd < 0) {
                printf("Device file opening error.\n");
                exit(1);
        }
        printf("r = read from device\n w = write to device\n enter command:");
        scanf("%c", &ch);

        switch(ch)
        {
                case 'w':
                        printf("enter data less than 100 characters:");
                        scanf("%[^\n]", wbuf);
                        write(fd, wbuf, sizeof(wbuf));
                        break;

                case 'r':
                        read(fd, rbuf, sizeof(wbuf));
                        printf("data read from device:%s\n", rbuf);
                        break;
        }

        return 0;
}

以上程序编译无任何错误。但是，当我以大小写'w'执行程序时，控件不会出现在“ scanf（”％[^ \ n]“，wbuf）;” 语句中，而不是该命令提示符是如下所示。

输出：

[root@localhost char_cdev]# ./a.out 
r = read from device
w = write to device
enter command:w
enter data less than 100 characters:[root@localhost char_cdev]#