@[TOC]第四章(选择结构和条件判断）

@[TOC]第四章(选择结构和条件判断）
例4.1

 # include<stdio.h>
 #include<math.h>
 int main ()
 {
   double a,b,c,disc,x1,x2,p,q;
   scanf("%lf%lf%lf",&a,&b,&c);
   disc=b*b-4*a*c;
   if(disc<0)
   printf("This equation hasn't real roots\n");
   else 
   {
     p=-b/(2.0*a);
     q=sqrt(disc)/(2.0*a);
     x1=p+q;
     x2=p-q;
     printf("real roots :\nx1=%7.2f\nx2=%7.2f\n",x1,x2);
     }
     return 0;
     }

运行结果如下：

例4.2

   # include<stdio.h>
 int main ()
 {float a,b,t;
 scanf("%f,%f",&a,&b);
 if(a>b)
 {
   t=a;
   a=b;
   b=t;
   }
   printf("%5.2f,%5.2f\n",a,b);
   return 0;
   }

运行结果如下：

例4.3

 # include<stdio.h>
 int main ()
 {
    float a,b,c,t;
    scanf("%f,%f,%f",&a,&b,&c);
    if(a>b)
    {
    t=a;
    a=b;
    b=t;
    }
    if(a>c)
    {
     t=a;
     a=c;
     c=t;
     }
     if(b>c)
     {
     t=b;
     b=c;
     c=t;
     }
     printf("%5.2f,%5.2f,%5.2f\n",a,b,c);
     return 0;
     } 

运行结果如下：

例4.4

    # include<stdio.h>
 int main ()
 {
  char ch;
  scanf("%c",&ch);
  ch=(ch>='Á'&&ch<='z')?(ch+32):ch;
  printf("%c\n",ch);
  return 0;
}

运行结果如下：

例4.5

  # include<stdio.h>
 int main ()
 {
   int x,y;
   scanf("%d",&x);
   if(x>==0)
   if(x>0) y=1;
   else y=0;
   else y=-1;
   printf("x=%d,y=%d\n",x,y);
   return 0;
   }

运行结果如下：

例4.6

 # include<stdio.h>
 int main ()
 {
  char grade;
  scanf("%c",&grade);
  printf("Your score:");
  switch(grade)
  {
    case'A':printf("85~100\n");break;
    case'B':printf("70~84\n");break;
    case'C':printf("60~69\n");break;
    case'D':printf("<60\n");break;
    default:printf(enter data error !\n");
    }
    return 0;
    }

运行结果如下：

例4.7

 # include<stdio.h>
 int main ()
 {
  void action1(int,int),action2(int,int);
  char ch;
  int a=15,b=23;
  ch=getchar();
  switch (ch)
  {
    case'a':
    case'A':action1(a,b);break;
   case'b':
   case'B':action2(a,b);break;
   default:putchar('\a');
   }
   return 0;
   }
   void action1(int x,int y)
   {
   printf("x+y=%d\n",x+y);
   }
   void action2(int x,int y)
   {
    printf("x*y=%d\n",x*y);
    }

运行结果如下：

例4.8

 # include<stdio.h>
 int main ()
 {int year,leap;
 printf("enter 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：

例4.9

 # include<stdio.h>
 #include<math.h>
 int main ()
 {
   double  a,b,c,disc,x1,x2,reapart,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 realroots:%8.4f and %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：

例4.10

 # include<stdio.h>
 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：