实验三

//任务1
#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+%.2fi,x2=%.2f-%.2fi\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;
} 

//ex2
#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;
}

//ex3
#include <stdio.h>
#include <math.h>
int main(){
    int a,b,n;
    n=0;
    for(a=101;a<=200;a++){
        for(b=2;b<=sqrt(a);b++){
            if(a%b==0)
               break;
            else if(b>sqrt((double)a)-1){
                printf("%d,",a);
                n++;
                if(n%5 ==0){
                    printf("\n");        
                }    
            }
            else
            continue;
        }
    }
    printf("\n101~200之间一共有%d个素数",n);
    return 0;
}

//Ex4
#include <stdio.h>
#include <math.h>
int main(){
    long n;
    printf("Enter a number:");
    while(scanf("%ld",&n)!=EOF){
        long a=0;
        int b=0;
        while (n!=0){
            if(n%2!=0){
                a=a+pow(10,b)*(n%10);
                b++;
            }
            n=n/10;
        }
        printf("new number is:%ld\n\n",a);
        printf("Enter a number:");
    }
    return 0;
} 

//Ex5
#include <stdio.h>
#include<math.h>
int main(){
    int n;
    printf("Enter n(1~9):");
    while(scanf("%d",&n)!=EOF){
        double s=0.0;
        double k=1.0;
        for(int a=1;a<=n;a++){
            k=k*a;
            s+=pow(-1,a-1)*(1.0/k);
        }
        printf("n=%d,s=%lf\n\n",n,s);
        printf("Enter n(1~9):");
    } 
    return 0;
} 

//Ex6
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
int main(){
    int day,n;
    srand(time(0));
    printf("猜猜12月哪一天是你的lucky day：");
    n=rand()%31+1;
    int a=0;
    while(scanf("%d",&day)!=EOF){
    a++;
    if(day==n){
        printf("Yes!");
        break;
    }
    if(day<n){
        printf("Too early!\n\n");
        printf("Try again:");
    }
    if(day>n){
        printf("Too late!\n\n");
        printf("Try again:");
    }
    if(a==3){
        printf("Your lucky day is%d",n);
        break;
    }
}
    return 0;
}