实验三

#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>
# include <stdlib.h>
int main()
{
    int n,m,i;
    for(n=101;n<=200;n++)
    {
        m=sqrt(n);
        for(i=2;i<=m;i++)
        if(n%i==0)break;
        if(i>m&&n>1)
        printf("%d ",n);
        else continue;
    }
    return 0;
    
}

# include <stdio.h>
int main() 
{
    int s,n,x,m;
    while(scanf("%d",&s)!=EOF)
    {
        m=0;
        x=1;
        for(s=s;s/10!=0;s=s/10)
        {
         n=s%10;
         if(n%2!=0)
         {
             m=m+n*x;
             x=x*10;
         }
         else continue;
        }
        printf("new number is:%d",m);
    }
    
    return 0;
}

# include <stdio.h>
int main()
{
    double i,n,x,m,s;
    while(scanf("%lf",&n)!=EOF)
    {
        s=0;
        for(i=1;i<=n;i++)
        {
            x=double(1/i);
            for(m=i-1;m!=0;m--)
            {
                x=x/m;
                if(int(i)%2==0);
                x=-x;
            }
            s+=x;
        }
        printf("n=%lf,s=%lf",n,s);
    }
}

# include <stdio.h>
# include <time.h>
# include <stdlib.h>
int main()
{
    int d,i,x;
    i=1;
    srand(time(0));
    x=1+rand()%30;
    printf("猜猜2020年12月哪一天会是你的lucy day\n");
    printf("开始了你有三次猜的机会\n");
    do
    {
        scanf("%d",&d);
        if(d==x)
        {
        printf("你猜对啦!\n");
        break;
        }
        else if(d<x)
        {
            printf("你猜的日期早了\n");
            printf("再猜\n");
            i++;
            continue;
         } 
        else
        {
        printf("你猜的日期晚了\n");
        printf("再猜\n");
        i++;
        continue;
        
        }
    }while(i<=3);
    if(i=4)
    printf("三次机会用完了，告诉你日期为%d号",x);
    return 0;
    
}