您当前的位置: get_choice函数要求输入字母A、B、C、D、Q或者a、b、c、d、q，其他均为非法输入，返回字母a、b、c、d、q。
但是，在第二次以及其后输入字母的时候，不管输入其他什么都会提示“Please input A, B, C, D, Q or a, b, c, d, q.”，需要再次输入才能进行判断；
get_first函数是教材上的一个实例，在该示例中是可以略过回车的，在这里就不行了。
- C/C++ code
int get_choice(void)
{
int ch;
printf("Please the operation of your choice:\n");
printf("A.add \tB.subtract\n");
printf("C.multiply\tD.divide\n");
printf("Q.quit\n");
ch=get_first();
while((ch<'a'||ch>'d')&&(ch<'A'||ch>'D')&&ch!='q'&&ch!='Q'){
printf("Please input A, B, C, D, Q or a, b, c, d, q.\n");
//不是首次输入的话，任何输入都需要输入两次
ch=get_first();
}
if((ch>='A'&&ch<='D')||ch=='Q')
ch+=32;
return ch;
}
int get_first(void)
{
int ch;
ch=getchar();
while(getchar()!='\n')
continue;
return ch;
}
A.add B.subtract
C.multiply D.divide
Q.quit
a
Please input a float number: 2
Please input a float number: 3
2.0 + 3.0 = 5.0.
Please the operation of your choice:
A.add B.subtract
C.multiply D.divide
Q.quit
b
Please input A, B, C, D, Q or a, b, c, d, q.
b
Please input a float number: 6
Please input a float number: 4
6.0 - 4.0 = 2.0.
Please the operation of your choice:
A.add B.subtract
C.multiply D.divide
Q.quit
c
Please input A, B, C, D, Q or a, b, c, d, q.
c
Please input a float number: 3
Please input a float number: 0
3.0 * 0.0 = 0.0.
Please the operation of your choice:
A.add B.subtract
C.multiply D.divide
Q.quit
d
Please input A, B, C, D, Q or a, b, c, d, q.
d
Please input a float number: 6
Please input a float number: 8
6.0 / 8.0 = 0.8.
Please the operation of your choice:
A.add B.subtract
C.multiply D.divide
Q.quit
q
Please input A, B, C, D, Q or a, b, c, d, q.
q
还有，在教材上的那个实例中，get_first函数中如果把ch=getchar();放到while语句中写成while((ch=getchar())!='\n')就不能正确响应，请问为什么。
附教材实例：
- C/C++ code
/**++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
*实例8.8，混合输入字符和数值；菜单技术，使用switch分支语句
*++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
*/
#include <stdio.h>
char get_choice(void);
char get_first(void);
char get_first(void);
void count(void);
int main(void)
{
int choice;
while((choice=get_choice())!='q'){
switch(choice){
case 'a':printf("Buy low, sell high.\n");
break;
case 'b':putchar('\a');
break;
case 'c':count();
break;
default :printf("Program error!\n");
break;
}
}
printf("Bye!\n");
return 0;
}
char get_choice(void)
{
int ch;
printf("Enter the letter of your choice:\n");
printf("a.advice\tb.bell\n");
printf("c.count \tq.quit\n");
ch=get_first();
while((ch<'a'||ch>'c')&&ch!='q'){
printf("Please input a, b, c or q: \n");
ch=get_first();
}
return ch;
}
char get_first(void)
{
int ch;
ch=getchar();
while(getchar()!='\n')
continue;
return ch;
}
char get_int(void)
{
int input;
char ch;
while(scanf("%d",&input)!=1){
while((ch=getchar())!='\n')
putchar(ch);
printf(" is not an integer, please enter agin.\n");
}
return input;
}
void count(void)
{
int n,i;
printf("Count how for? Enter an integer: \n");
n=get_int();
for(i=1;i<=n;i++)
printf("%d\n",i);
while(getchar()!='\n')
continue;
}