实验3

#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;
}

#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;
}

#include<stdio.h>
#include<math.h>
int main(){
    int n,i,m;
    double k;
    m=0;
    for(n=101;n<=200;n++){
       k=sqrt(n);
       for(i=2;i<=k;i++){
        if(n%i==0)
        break;
       }
       if(i>k){
           printf("%5d",n);
           m++; 
       }
    }
    printf("\n");
    printf("101~200之间共有%d个素数\n",m);
    return 0;
}

#include<stdio.h>
int main(){
    long s;
    int m,sum,i;
    i=1;
    printf("Enter a number:");
    while(scanf("%ld",&s)!=EOF){
        while(s>0){
            m=s%10;
            if(m%2!=0){
                sum+=m*i;
                i*=10;
            }
            s=s/10;
        }
        printf("new number is:%d\n",sum);
        printf("Enter a number:");
    }
    return 0;
}

#include<stdio.h>
#include<math.h>
int main(){
    int n,i,m;
    float s;
    printf("Enter n(1~10):");
    while(scanf("%d",&n)!=EOF){
        s=0.0;
        m=1;
        for(i=1;i<=n;i++){
            m*=i;
            s+=pow(-1,i-1)/m;    
        }
        printf("n = %d,s = %f\n",n,s);
        printf("Enter n(1~10):");
    }
    return 0;        
} 

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main(){
    int n,x,m;
    printf("猜猜2020年12月哪一天会是你的luck day\n");
    srand(time(0));
    m=(rand()%(31-1+1))+1;
    x=1;
    printf("%d\n",m);
    printf("开始喽。你有三次机会，猜吧(1~31):");
    do{
        scanf("%d",&n);
        if(n==m)
           break;
        else if(n<m){
            printf("你猜的日期早了，luck day还没到呢\n");
            x++;
        }
        else{
            printf("你猜的日期晚了，luck day悄悄溜到前面啦\n");
            x++; 
        }   
        if(x<3)    
            printf("再猜(1~31):");
    }while(x<=3);
    if(x>3){
        printf("次数用完啦。偷偷告诉你：12月，你的luck day是%d号",m);
    }
    return 0;
}