求教，为什么Enter you choice(a,b,c,d):会打印两次？

int main(void)
{
char c;
float salary=0, tax;
do {
printf("Enter you choice(a,b,c,d):\n");
scanf("%c", &c);
switch (c)
{
case 'a':
printf("Enter salary before tax:\n");
scanf("%f", &salary);
tax = 17850 * base + (salary - 17850)*extra;
printf("you tax is:%.2f\n", tax);
break;
case'b':
printf("Enter salary before tax:\n");
scanf("%f", &salary);
tax = 23900 * base + (salary - 23900)*extra;
printf("you tax is:%.2f\n", tax);
break;
case'c':
printf("Enter salary before tax:\n");
scanf("%f", &salary);
tax = 29750 * base + (salary - 29750)*extra;
printf("you tax is:%.2f\n", tax);
break;
case'd':
printf("Enter salary before tax:\n");
scanf("%f", &salary);
tax = 14875 * base + (salary - 14875)*extra;
printf("you tax is:%.2f\n", tax);
break;
}
} while (c != 'e');
return 0;
}