//一元二次方程求解
//重複執行，直到按ctrl+z2結束
//
#include <math.h>
#include<stdio.h>
   
int main(){
    
    
   float a,b,c,x1,x2;
   float delta,real,imag;
   
  printf("Enter a, b, c: ");
   
   while(scanf("%f%f%f",&a,&b,&c)!=EOF){
       if(a==0)
        printf("not quadratic equation.\n\n");
        
 
else{
            delta =b*b-4*a*c;
            
            if(delta>=0){
                x1=(-b+sqrt(delta)) / (2*a);
                x2=(-b-sqrt(delta))/(2*a);
                printf("x1=%.2f,x2=%.2f\n\n",x1,x2);
            }
            else{
                real=-b/(2*a);
                imag=sqrt(-delta)/(2
 
*a);
                printf("x1=%.2f+%.2fi,x2=%.2f-%.2fi\n\n",real,imag,real,imag);
                
            }
        }
        printf("Enter a,b,c:");
   } 
   return 0;
}

// 生產n個0~9之間的隨機整數，並列印輸出
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#define N 5

int main(){
    
 
int x,n;
    
    srand(time(0));
    n=0;
    do{
     n++;
     x=rand()%10;
     printf("%3d",x);
    }while(n<N);
    
    printf("\n");
    
    return 0;
} 

//判斷素數 
#include<stdio.h>
int main(){
    int i,j,m;
  
    for(i=100;i<=200;i++) 
    {for(j=2;j<i;j++)
       {if(i%j==0) break;
       }
       if(j>=i)
       printf("%d\t",i);
       m++;
       
    }
    }

#include<stdio.h>
#include<math.h>
 int main(){
     int x,y;
     scanf("%d",&y);
     double z=1.0,s=0.0;
     for(x=1;x<=y;x++){
         if(x%2==0){
             z=-(x*z);
             
         } else{z=abs(x*z);
             
         }
         
         s+=1.0/z;
     }printf("%lf",s);
     
 }
     

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main()
{
    int x,n,i;
    srand(time(0));
    n=0;
    x=rand()%31;
        printf("那天是luck day\n\n");
        printf("開始樓，你有三次機會，彩筆(1~31): ");
    for(i=1;i<=3;++i){
    if(i>=2){
        printf("再猜:"); 
    }
    scanf("%d",&n);
    printf("\n");
     if(n<x){
            printf("早了,luck day還沒到\n\n");
        }
         if(n==x){
            printf("你猜對了");
            break;
        }
         if(n>x){
            printf("你猜的日期晚了,luck day悄悄溜到後面拉\n\n");
        }
        

    if(i==3){
            printf("次數用完啦,悄悄告訴你,12月,luck day是%d號",x);
        }
        }
    printf("\n\n");
    return 0;
}

#include<stdio.h>
int main(){
    int x,y,z,m,k=0,s,a,b,c,l;
    scanf("%d",&s);
    while(s!=0){
        x=s%10;
        if(x%2==1){
            m=x;
            k=10*k+m;
        }
        s=s/10;
    }a=k%10;
    b=k/10%10;
    c=k/100;
    l=a*100+b*10+c;
    printf("%d",l);
    return 0;
}