计算器程序完善修改优化

Question

题目要求：编写一个程序，显示一个菜单，为您提供加法、减法、乘法或除法的选项，获得您的选择后，该程序请求两个数，然后执行您选择的操作，该程序应该只接受它所提供的菜单选项，它应该使用float类型的数，并且如果用户未能输入数字应允许其重新输入，在除法的情况中，如果用户输入0作为第二个数，该程序应该提示用户输入一个新的值。

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
float add(float a, float b);
float subtract(float a, float b);
float multiply(float a, float b);
float divide(float a, float b);
void operation_menu(void);
char get_first(void);
int main(void)
{
    float num1, num2;
    int ch;
    char str[40];
    printf_s("Enter the operation of your choice:\n");
    operation_menu();
    ch = get_first();
    while (ch!='q')
    {
        switch (ch)
        {
        case 'a':
            printf_s("Enter first number:");
            while (scanf_s("%f", &num1) != 1)
            {
                gets_s(str);
                printf_s("%s is not an number.\n", str);
                printf_s("Please enter a number,such as 2.5,-1.78E8,or 3:");
            }
            printf_s("Enter second number:");
            while (scanf_s("%f", &num2) != 1)
            {
                gets_s(str);
                printf_s("%s is not an number.\n", str);
                printf_s("Please enter a number,such as 2.5,-1.78E8,or 3:");
            }
            printf_s("%.2f+%.2f=%.2f\n",num1,num2,add(num1,num2));
            break;
        case 's':
            printf_s("Enter first number:");
            while (scanf_s("%f", &num1) != 1)
            {
                gets_s(str);
                printf_s("%s is not an number.\n", str);
                printf_s("Please enter a number,such as 2.5,-1.78E8,or 3:");
            }
            printf_s("Enter second number:");
            while (scanf_s("%f", &num2) != 1)
            {
                gets_s(str);
                printf_s("%s is not an number.\n", str);
                printf_s("Please enter a number,such as 2.5,-1.78E8,or 3:");
            }
            printf_s("%.2f-%.2f=%.2f\n", num1, num2, subtract(num1, num2));
            break;
        case 'm':
            printf_s("Enter first number:");
            while (scanf_s("%f", &num1) != 1)
            {
                gets_s(str);
                printf_s("%s is not an number.\n", str);
                printf_s("Please enter a number,such as 2.5,-1.78E8,or 3:");
            }
            printf_s("Enter second number:");
            while (scanf_s("%f", &num2) != 1)
            {
                gets_s(str);
                printf_s("%s is not an number.\n", str);
                printf_s("Please enter a number,such as 2.5,-1.78E8,or 3:");
            }
            printf_s("%.2f*%.2f=%.2f\n", num1, num2, multiply(num1, num2));
            break;
        case 'd':
            printf_s("Enter first number:");
            while (scanf_s("%f", &num1) != 1)
            {
                gets_s(str);
                printf_s("%s is not an number.\n", str);
                printf_s("Please enter a number,such as 2.5,-1.78E8,or 3:");
            }
            printf_s("Enter second number:");
            while (scanf_s("%f", &num2) != 1)
            {
                gets_s(str);
                printf_s("%s is not an number.\n", str);
                printf_s("Please enter a number,such as 2.5,-1.78E8,or 3:");
            }
            if (num2==0)
            {
                printf_s("!Please enter another number that does't include 0.\n");
                scanf_s("%f", &num2);
            }
            printf_s("%.2f/%.2f=%.2f\n", num1, num2, divide(num1, num2));
            break;
        default:
            printf_s("Please enter the characters of a、s、m、d or q\n");
            ch = get_first();
            continue;
        }
        printf_s("Enter the operation of your choice:\n");
        operation_menu();
        ch = get_first();
    }
    printf_s("Bye.\n");
    system("pause");
    return 0;
}
char get_first(void)
{
    int ch;
    ch = getchar();
    while (isspace(ch))
    {
        ch = getchar();
    }
    while (getchar()!='\n')
    {
        continue;
    }
    return ch;
}
void operation_menu(void)
{
    printf_s("a.add               s.subtract\n");
    printf_s("m.multiply          d.divide\n");
    printf_s("q.quit\n");
}
float add(float a,float b)
{
    float add_result;
    add_result = a + b;
    return add_result;
}
float subtract(float a, float b)
{
    float sub_result;
    sub_result = a - b;
    return sub_result;
}
float multiply(float a, float b)
{
    float mult_result;
    mult_result = a*b;
    return mult_result;
}
float divide(float a, float b)
{
    float div_result;
    div_result = a / b;
    return div_result;
}

程序执行可以，请问是否可以修改程序使其更加简洁，但需要完成所有内容，并且更加用户友好。谢谢，欢迎大家讨论
2015/5/20
今日探索，代码正式修改为下面，欢迎指正

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
void operation_menu();
char get_first();
float get_float();
char get_choice();
int main(void)
{
    float num1, num2;
    char ch;
    printf_s("Enter the operation of your choice:\n");
    operation_menu();
    while ((ch=get_choice())!='q')
    {
        printf_s("Enter first number:");
        num1 = get_float();
        printf_s("Enter second number:");
        num2 = get_float();
        while (ch == 'd'&&num2 == 0)
        {
            printf_s("!Please enter another number that does't include 0.\n");
            num2 = get_float();
        }
        switch (ch)
        {
        case 'a':
            printf_s("%.2f+%.2f=%.2f\n", num1, num2, (num1 + num2));
            break;
        case 's':
            printf_s("%.2f-%.2f=%.2f\n", num1, num2, (num1 - num2));
            break;
        case 'm':
            printf_s("%.2f*%.2f=%.2f\n", num1, num2, (num1*num2));
            break;
        case 'd':
            printf_s("%.2f/%.2f=%.2f\n", num1, num2, (num1 / num2));
            break;
        default:
            break;
        }
        printf_s("Enter the operation of your choice:\n");
        operation_menu();
    }
    printf_s("Bye.\n");
    system("pause");
    return 0;
}
//获取第一个字符
char get_first()
{
    int ch;
    ch = getchar();
    while (isspace(ch))
    {
        ch = getchar();
    }
    while (getchar()!='\n')
    {
        continue;
    }
    return ch;
}
//打印菜单选项
void operation_menu()
{
    printf_s("a.add               s.subtract\n");
    printf_s("m.multiply          d.divide\n");
    printf_s("q.quit\n");
}
//获取数字
float get_float()
{
    float num;
    char str[40];
    while (scanf_s("%f",&num)!=1)
    {
        gets_s(str);
        printf_s("%s is not a number.\n",str);
        printf_s("Please enter a number,such as 2.5,-1.78E8,or 3:");
    }
    while (getchar()!='\n')
    {
        ;
    }
    return num;
}
//选择函数
char get_choice()
{
    char choice;
    choice = get_first();
    while (choice!='a'&&choice!='s'&&choice!='m'&&choice!='d'&&choice!='q')
    {
        printf_s("Please response with a,s,m,d or q.\n");
        choice = get_first();
    }
    return choice;
}

Answer 1

你可以用C++或者C的图形库做个计算器，这样你对布局，消息机制，MVC概念都会有进一步的认识，控制台程序主要是用来验证算法的，没必要这样。