实验三

#include<stdio.h>
#include<math.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 m,i,k,j,h=0,leap=1;
    for(m=101;m<=200;m++)
    {
        k=sqrt(m+1);
        for(i=2;i<=k;i++)
        if(m%i==0)
        {
            leap=0;
            break;
        }
        if(leap)
        {
            printf("%4d",m);
            h++;
            if(h%5==0)
            printf("\n");
        }
        leap=1;
    }
    printf("\n");
    printf("100~200之间共有%d个素数.\n",h);
    return 0;
}

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

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int main()
{
    int n,i;
    
    printf("Enter n(1~10): ");
    while(scanf("%d",&n)!=EOF){
    double k,s=0.0,t=1.0;
    for(i=1;i<=n;i++)
    {
        if(i%2!=0)
        {
            t=abs(t*i);
        }else{
            t=-(t*i);
        }
        s+=1.0/t;
    }

    printf("n=%d,s=%lf\n\n",n,s);
    printf("Enter n(1~10): ");
}
    return 0;
}

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main()
{
    int x,n,i;
    srand(time(0));
    n=0;
    x=rand()%31;
        printf("猜猜哪一天会是你的luck day\n\n");
        printf("开始喽，你有三次机会，猜吧(1~31): ");
    for(i=1;i<=3;++i){
    if(i>=2){
        printf("再猜："); 
    }
    scanf("%d",&n);
    printf("\n");
     if(n<x){
            printf("你猜的日期早了，luck day还没到呢\n\n");
        }
         if(n==x){
            printf("你猜对了");
            break;
        }
         if(n>x){
            printf("你猜的日期晚了，luck day悄悄溜到前面啦\n\n");
        }
        

    if(i==3){
            printf("次数用完啦，悄悄告诉你，12月，你的luck day是%d号",x);
        }
        }
    printf("\n\n");
    return 0;
}