第四章 选择结构程序设计3

例4.8 写一程序，判断某一年是否为闰年

#include
int main()
{
int year ,leap;
printf("enter year:");
scanf("%d",&year);
if(year%4==0)
{
if(year%100==0)
{
if(year%400==0)
leap=1;
else
leap=0;
}
else
leap=1;
}
else
leap=0;
if(leap)
printf("%d is",year);
else
     printf("%d is not",year);
     printf("a leap year.\n");
     return 0;
     }

运行结果如下：
第二次运行结果

程序改写

    #include
    int main()
    {
    int leap,year;
    printf("enter year:);
    scanf("%d",&year);
    if(year%4==0&&year%100!=0)||(year%400==0))
    leap=1;
    else
    leap=0;
    if(leap)
    printf("%d is ",year);
    else
    printf("%d ia not",year);
    printf("a leap year.\n");
    return 0;
    }
    
   
    

运行结果如下：

例4.9 求二次方程的解

#include
#include
int main()
{
double a,b,c,disc,x1,x2,realpart,imagpart;
scanf("%lf%lf%lf",&a,&b,&c);
printf("The equation:");
if(fabs(a)<=1e-6)
printf("is not a quadratic\n");
else
{
disc=b*b-4*a*c;
if(fabs(disc)<=1e-6)
printf("has two equal roots:%8.4f\n"，-b/(2*a));
else
if(disc>1e-6)
{
x1=(-b+sqrt(disc)/(2*a);
x2=(-b-sqrt(disc)/(2*a);
printf("has distinct real roots : %8.4fand%8.4f\n",x1,x2);
}
else
{
realpart=-b/(2*a);
imagpart=sqrt(-disc)/(2*a);
printf("has complex roots:\n");
printf("%8.4f+%8.4fi\n",realpart,imagpart);
printf("%8.4f-%8.4fi\n",realpart,imagpart);
}
}
return 0;
}

运行结果如下：（运行3次）

例4.10计算运输费用

#include
int main()
{
int c,s;
float p,w,d,f;
printf("please enter price ,weight,discount");
scanf(%f%f%d",&p,&w,&s);
if(s>=3000)c=12;
else        c=s/250;
switch(c)
{
  case 0:d=0;break;
  case 1:d=2;break;
  case 2:
  case 3:d=5;break;
  case 4:
  case 5：
  case 6:
  case 7:d=8;break;
  case 8:
  case 9:
  case 10:
  case 11:d=10;break;
  case 12:d=15;break;
  }
  f=p*w*s*(1-d/100);
  printf("freight=%10.2f\n",f);
  return 0;
  }

运行结果如下：