简单加减乘除

#include <stdio.h>
#include <string.h>

char get_choice(void);
char get_first(void);
float get_float(void);
void add(void);
void subtract(void);
void multiply(void);
void divide(void);

int main(void)
{
   int choice;

   while((choice=get_choice())!='q')
   {
      switch (choice)
      {
      case 'a':
         add();
         break;
      case 'b':
         subtract();
         break;
      case 'c':
         multiply();
         break;
      case 'd':
         divide();
         break;
      case 'q':
         break;
      }
   }
   return 0;
}

char get_choice(void)
{
   int ch;

   printf("input the letter of your choice:\n");
   printf("a. add\nb. subtract\nc. multiply\nd. divide\nq. quit\n");
   ch = get_first();
   while((ch<'a' || ch>'d') && ch!='q')
   {
      printf("please respond with a,b,c,d,q:");
      ch = get_first();
   }

   return ch;
}

char get_first(void)
{
   int ch;

   ch = getchar();
   while(getchar()!='\n')
      continue;

   return ch;
}

float get_float(void)
{
   float input;
   char ch;

   while(scanf("%f",&input) != 1)
   {
      while((ch=getchar()) != '\n')
         putchar(ch);
      printf("is not a float number.\n");
      printf("please input a float number,such as 1.1, 2.5:");
   }
   return input;
}

void add(void)
{
   float f_num,s_num;

    printf("input first number:");
    f_num = get_float();
    printf("input second number:");
    s_num = get_float();
    printf("%f + %f = %f\n",f_num,s_num,f_num+s_num);
}

void subtract(void)
{
   float f_num,s_num;

    printf("input first number:");
    f_num = get_float();
    printf("input second number:");
    s_num = get_float();
    printf("%f - %f = %f\n",f_num,s_num,f_num-s_num);
}

void multiply(void)
{
   float f_num,s_num;

    printf("input first number:");
    f_num = get_float();
    printf("input second number:");
    s_num = get_float();
    printf("%f * %f = %f\n",f_num,s_num,f_num*s_num);
}

void divide(void)
{
   float f_num,s_num;

    printf("input first number:");
    f_num = get_float();
    printf("input second number:");
    s_num = get_float();
   if(s_num == 0)
   {
      printf("input a number other than 0:");
      s_num = get_float();
   }
    printf("%f / %f = %f\n",f_num,s_num,f_num/s_num);
}