C primer 第七章分支和跳转 习题7.8

#include <stdio.h>
#define RATE_BASE_300 0.15f
#define RATE_300_TO_450 0.2f
#define RATE_FLOW 0.25f
int main(void)
{
    int hour,choice;    
    float tax_300=300*RATE_BASE_300;
    float tax_450=tax_300+150*RATE_300_TO_450;
    float tax,pay,after_pay,d_per_hour;

    printf("*****************************************************************\n");
    printf("Enter the number corresponding to the desired pay rate or action:\n");
    printf("1)$8.75/hr                2)$9.33/hr\n");
    printf("3)$10.00/hr               4)$11.20/hr\n");
    printf("5)quit\n");
    printf("*****************************************************************\n");
    
    while (scanf("%d",&choice)==1)
    {
        if (choice<=5 && choice>=1) //控制输入为1~5
        {
            switch(choice)
            {
            case 1:
                d_per_hour=8.75f;
                break;
            case 2:
                d_per_hour=9.33f;
                break;
            case 3:
                d_per_hour=10.0f;
                break;
            case 4:
                d_per_hour=11.20f;
                break;
            default: goto end;
            }
        }
        else {
            printf("Enter the correct num.\n");
            continue; //输入不是1~5时 自动转到循环最开始
        }    
        printf("How many hours you work per week:");
        scanf("%d",&hour);
        pay=d_per_hour*hour*4;
        if (pay<=300)
            tax=RATE_BASE_300*pay;
        else if (pay<=450)
            tax=tax_300+(pay-300)*RATE_300_TO_450;
        else 
            tax=tax_450+(pay-450)*RATE_FLOW;
        after_pay=pay-tax;    
        printf("You total salary is %.2f,and after tax it is %.2f.That means you have pay $%.2f tax\n",pay,after_pay,tax);

        printf("*****************************************************************\n");
        printf("Enter the number corresponding to the desired pay rate or action:\n");
        printf("1)$8.75/hr                2)$9.33/hr\n");
        printf("3)$10.00/hr               4)$11.20/hr\n");
        printf("5)quit\n");
        printf("*****************************************************************\n");

    }
    end:
    return 0;
}

 

1.使用一个switch语句做选项时，如果希望能退出程序，可以用goto语句。

   goto stop;
   stop: 
   return 0;

其他时候不推荐用goto语句。

 

改进如下：

#include <stdio.h>
#define RATE_BASE_300 0.15f
#define RATE_300_TO_450 0.2f
#define RATE_FLOW 0.25f
int get_choice(void);
int main(void)
{
    int hour,choice;    
    float tax_300=300*RATE_BASE_300;
    float tax_450=tax_300+150*RATE_300_TO_450;
    float tax,pay,after_pay,d_per_hour;
    
    while (choice=get_choice())
    {
        if (choice<=5 && choice>=1) //控制输入为1~5
        {
            switch(choice)
            {
            case 1:
                d_per_hour=8.75f;
                break;
            case 2:
                d_per_hour=9.33f;
                break;
            case 3:
                d_per_hour=10.0f;
                break;
            case 4:
                d_per_hour=11.20f;
                break;
            default: goto end;
            }
        }
        else {
            printf("Enter the correct num.\n");
            continue; //输入不是1~5时 自动转到循环最开始
        }    
        printf("How many hours you work per week:");
        scanf("%d",&hour);
        pay=d_per_hour*hour*4;
        if (pay<=300)
            tax=RATE_BASE_300*pay;
        else if (pay<=450)
            tax=tax_300+(pay-300)*RATE_300_TO_450;
        else 
            tax=tax_450+(pay-450)*RATE_FLOW;
        after_pay=pay-tax;    
        printf("You total salary is %.2f,and after tax it is %.2f.That means you have pay $%.2f tax\n",pay,after_pay,tax);
        
    }
  end:
    return 0;
}

int get_choice(void)
{
    int num;
    printf("*****************************************************************\n");
    printf("Enter the number corresponding to the desired pay rate or action:\n");
    printf("1)$8.75/hr                2)$9.33/hr\n");
    printf("3)$10.00/hr               4)$11.20/hr\n");
    printf("5)quit\n");
    printf("*****************************************************************\n");
    scanf("%d",&num);

    return num;

}

2.改进主要集中在输入选项的显示，减少了代码量，并且使得程序可读性增强。每次进入循环都会显示选项。下一步改进将集中于在get_choice函数中实现对输入的控制，对不正确的输入进行提示。