C语言实例:键盘输入一个算术的运算式子，输出运算结果

#include<stdio.h>
#include<math.h>

int main(void)
{
    /*init 0.0*/
    double a = 0.0;
    double b = 0.0;
   
    char op = '0';    /* + - * / ^*/
   
    printf("Enter a expression:");
    /*must be %lf beacuse we use double*/
    scanf("%lf%c%lf",&a,&op,&b);
   
    switch(op)
    {
        case '+':
            printf("%.2f + %.2f = %.3f",a,b,(a+b));
            break;
        case '-':
            printf("%.2f - %.2f = %.3f",a,b,(a-b));
            break;
        case '*':
            printf("%.2f * %.2f = %.3f",a,b,(a*b));
            break;
        case '/':
            if (fabs(b-0.0) < 0.0000001)
            {
                printf("Input Err.\n");
                break;
            }
            printf("%.2f * %.2f = %.3f",a,b,(a/b));
            break;
        case '^':
            printf("%.2f ^ %.2f = %.3f",a,b,pow(a,b));
            break;
        default:
            printf("Input Err.\n");
    }
   
    return 0;

}

#include<stdio.h>

int main(void)
{
    int clths = 0;
    int trs = 0;
    int suit = 0;
    int money = 0;
   
    printf("Clothes:");
    scanf("%d",&clths);
    printf("Trousers:");
    scanf("%d",&trs);
   
    if (clths > trs)
    {
        suit = trs;
        if (suit >= 50)
        {
            money = suit * 80;
        }
        else
        {
            money = suit * 90;
        }
        money += (clths-trs)*60;
    }
    else
    {
        suit = clths;
        if (suit >= 50)
        {
            money = suit * 80;
        }
        else
        {
            money = suit * 90;
        }
        money += (trs-clths)*45;
    }
   
    printf("Money:%d",money);
   
    return 0;

}

#include<stdio.h>

int main(void)
{
    int year = 0;
    int month = 0;
    int day = 0;
    int past = 0;
   
    printf("Please Input a day(Eg.yyyy-mm-dd):");
    scanf("%d-%d-%d",&year,&month,&day);
   
    past += day;    /* 2011-3-6 = 6+28+31 =65 */
   
    /* 31 28 or 29 31 30 31 30 31 31 30 31 30 31 */
    /* no break; */
    switch(month-1)
    {
        case 12:
            past += 31;
        case 11:
            past += 30;
        case 10:
            past += 31;
        case 9:
            past += 30;
        case 8:
            past += 31;
        case 7:
            past += 31;
        case 6:
            past += 30;
        case 5:
            past += 31;
        case 4:
            past += 30;
        case 3:
            past += 31;
        case 2:
            if (((year%4==0)&&(year%100!=0))||(year%400==0))
            {
                past +=29;
                /* printf("leap\n"); */
            }
            else
            {
                past +=28;
            }
        case 1:
            past +=31;
        case 0:
            break;
        default:
            printf("Input may be wrong.");
            break;
    }
   
    printf("Today is %dth of %d:",past,year);
   
    return 0;

}