Example 4.1 Solving the Roots of axx+b*x+c=0 Equation

#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;
}

The results are as follows:

Example 4.2 Input two real numbers and output them in order from small to large

#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;
}

The results are as follows:

Example 4.3 Input three real numbers and output them in order from small to large

#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;
}

The results are as follows:

Example 4.4 Enter a character to determine if it is a capital letter. If it is converted to a lowercase letter, otherwise it will not be converted.

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

The results are as follows:

Example 4.5 has a step function y=-1 (x < 0) y = 0 (x = 0) y = 1 (x > 0)

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

The results are as follows:

Example 4.6 Requires the output of percentage scores according to the grade of the examination results

#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;
 }

The results are as follows:

Example 4.7 Processing menu commands with switch statements

#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);
}

The results are as follows:

Example 4.8 Write a program to determine whether a year is a leap year.

#include <stdio.h>
int main()	
{int year,leap;
  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 is not ",year);
    printf("a leap year.\n");
  return 0;
}

The results are as follows:

Example 4.9 Solution of axx+b*x+c=0

#include <stdio.h>
#include <math.h>
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:%8.4f 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;
}  

The results are as follows:

Example 4.10 Transport company calculates the transportation cost to the user. The farther the distance is, the lower the transportation cost is. The criteria are as follows: No discount for S < 250

250 <= s < 500 2% discount
500<=s<10005%discount
1000 <= s < 2000 8% discount
2000 <= s < 3000 10% discount
3000<=s 15% discount

#include<stdio.h>
int main()
{
	int c,s;
	float p,w,d,f;
	printf("Please enter unit price, weight, distance:");
	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("The total freight is:%10.2f\n",f);
	return 0;
}

The results are as follows: