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>
int fun(int n)
{
    int i;
    if (n==2||n==3)
        return 1;
    for (i=2;i<=sqrt(n);i++)
        {
            if (n%i==0)
                return 0;
        }
    return 1;
}
int main()
{
    int i,j=0,n;
    for (n=101;n<=200;n++)
    {
        if (fun(n)==1)
        {
            printf("%d\n",n);
            j++;
        }    
    }
    printf("101-200之间共有%d个素数",j);
    return 0;
}

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

#include <stdio.h>
double fun(int n)
{
    int i;
    double sum=1;
    for (i=1;i<=n;i++)
        sum*=i;
    return sum;
}
int main()
{
    int n,i;
    double s=0;
    printf("Enter n(1~10):");
    while(scanf("%d",&n)!=EOF)
    {
        s=0;
        for (i=1;i<=n;i++)
        {
            if(i%2==0)
                s-=1.0/fun(i);
            else
                s+=1.0/fun(i);
        }
        printf("n=%d,s=%lf\n",n,s);
        printf("Enter n(1~10):");
    }
}

#include <stdio.h> 
#include <stdlib.h> 
#include <time.h>  
int main() 
{ 
    int x, n,i,j,k; 
    srand(time(NULL)); 
    x = rand()%31+1;
    printf("猜一猜20202年12月那一天是你的luck day\n");
    printf("开始喽，你有三次机会，猜吧（1~31）:");
    for (i=0;i<=2;i++)
    {
        scanf("%d",&n);
        if (n>x)
            printf("你猜的日期晚了，lucky day 悄悄溜到前面啦！\n");
        else if (n<x)
            printf("你猜的日期早了，lucky day 还没到呢！\n");
        else
        {
            printf("你猜对啦!\n");
            return 0;
        }
        printf("再猜:");
    }
    printf("次数用完啦，悄悄告诉你，12月，你的lucky day是:%d\n",x);
    return 0;
}