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<stdlib.h>
int main(){
    int i,n; 
    int m = 0;
    for(n=101;n<=200;n++)
{
    for(i=2;i<=n-1;i++)
    {
    if(n%i==0) 
    break;}
    if(i==n)
        {
    printf("%d\n",n);
        m++;
}
        
}

printf("\n 101~200之间共有%d个素数",m);
     return 0;
}

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

#include<stdio.h>
#include<stdlib.h>
int main(){
    int n, i;
    double b, sum=1;
    int a=1;
    scanf("%d",&n);
    for(i=2;i<=n;i++)
{    
    a=(-1)*a*i;
    b=1.0/a;
    sum+=b;
    } 

    printf("%.6lf",sum); 
    
    return 0;
}

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include <time.h>
int main(){
    int  m, i;
    srand((int)time(0));
    int n=rand()%31;
    m=1;
    printf("猜猜2020年12月哪天会是你的luck day\n");
    printf("开始喽，你有三次机会，猜吧（1~31）：\n");
    scanf("%d",&i);
    while(m<=2){
        if(i<n)
{
    
    printf("你猜的日期早了， luck day还没到呢");
    scanf("%d",&i);
    m++; 
}
    else if(i>n)
{ 
    printf("你猜的日期晚了， luck day悄悄溜到前面啦");
    scanf("%d",&i);
    m++;
}
    else if(i==n)
{
    printf("恭喜，猜对啦\n");
    m++;
}

if(m>2)
    {
    printf("次数用完啦，偷偷告诉你：12月，你的luck day 是%d号",n);
}
}

            return 0;
}