为什么会是非法 continue？

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
float get_int (void);
char get_first (void);
char get_choice (void);
void get_add (void);
void get_sub (void);
void get_mul (void);
void get_div (void);
int main ()
{
char choice; while((choice = get_choice()) != 'q')
{
switch (choice)
{
case 'a': get_add ();
break;
case 's': get_sub ();
break;
case 'm': get_mul ();
break;
case 'd': get_div ();
break;
default: printf("proaram error.\n");
break;
}
}
printf("Bye.\n");
system("pause");
return 0;
}
char get_choice (void)
{
int ch;
printf("Enter the operation of your choice:\n");
printf("a. add s. subtract\t\nm. multiply");
printf(" d. divide\t\nq. quit\n");
ch = get_first ();
while(ch != 'a' && ch != 's' && ch != 'd' && ch != 'm' && ch != 'q')
{
printf("I understand your enter.\nPlease enter such as a, s, m, d or q.\n");
ch = get_first ();
}
return ch;
}
char get_first (void)
{
char ch; ch = getchar();
if (isspace (ch))
continue;
else
while (getchar() != '\n')
putchar(ch);
return tolower (ch);
} void get_add (void)
{
float f_num;
float s_num; printf("Enter first number: ");
f_num = get_int ();
printf("Enter second number: ");
s_num = get_int (); printf("%g + %g = %g \n", f_num, s_num, f_num - s_num);
} void get_sub (void)
{
float f_num;
float s_num;
printf("Enter first number: ");
f_num = get_int ();
printf("Enter second number: ");
s_num = get_int (); printf("%g + %g = %g\n", f_num, s_num, f_num - s_num);
} void get_mul (void)
{
float f_num;
float s_num; printf("Enter first number: ");
f_num = get_int ();
printf("Enter second number: ");
s_num = get_int (); printf("%g * %g = %g\n", f_num, s_num, f_num * s_num);
} void get_div (void)
{
float f_num;
float s_num; printf("Enter first number: ");
f_num = get_int ();
printf("Enter second number: ");
s_num = get_int ();
while ( s_num == 0)
{
printf ("Entet a number other than 0: ");
s_num = get_int ();
} printf("%g / %g = %g\n", f_num, s_num, f_num / s_num);
} float get_int (void)
{
float input;
char ch;
while(scanf ("%f", &input) != 1)
{
while ((ch = getchar ()) != '\n')
putchar(ch);
printf (" is not an number.\n");
printf ("Please enter such as 2.5, -1.78E8 or 3: ");
}
return input;
}


度娘排版有问题将就着看啊

找到原因了。。。。只能 在while， do while ， for 这三个循环中使用