加减乘除法（简单）,该怎么解决

加减乘除法（简单）
本来以为这题简单，不需要帮助了。。可是还是没法。。
麻烦过一下代码。。怎样实现输入选择后再输入数字？

C/C++ code

#include<stdio.h>float add(float,float);float subtract(float,float);float multiply(float,float);float divide(float,float);int main(void){float m,n;char ch;printf("Enter the operation of your choice.('q' to quit)\n");printf("a.add       b.subtract\n");printf("c.multiply  c.divide\n");while((ch=getchar())!='q')       //这里应该正确{    scanf("Enter first number:%f\n",&m);    scanf("Enter second number:%f\n",&n);//这俩个输入数字为什么就没出现？    if(ch=='a')        add(m,n);            else if(ch=='b')       subtract(m,n);    else if(ch=='c')        multiply(m,n);    else if(ch=='d')        divide(m,n);    else        break;    printf("Enter another operation of your choice.('q' to quit)\n");}return 0;}float add(float a,float b){    float num;    num=a+b;    printf("%f+%f=%f\n",a,b,num);    return 0;}float subtract(float a,float b){    printf("%f-%f=%f\n",a,b,a-b);    return 0;}float multiply(float a,float b){printf("%f*%f=%f\n",a,b,a*b);return 0;}float divide(float a,float b){    if(b==0)    {        printf("enter the second number(not 0):\n");            scanf("%f",&b);    }    else        printf("%f/%f=%f\n",a,b,a/b);    return 0;}