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>
int main(){
    
    int n,m,i=0,j=0,a=0;
    for(n=101;n<=200;n++){
        i=0;
        for(m=2;m<n;m++){
            if(n%m==0){
                i++;
            }
        }
        if(i==0){
            printf("%5d",n);
            j++;a++;
            if(j==5){
                printf("\n");
                j=0;
            }
        }
    }
    printf("\n101~200之间共有%d个素数\n",a);
    
    return 0;
} 

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

#include <stdio.h>
int main(){
    
    int n,m;

    printf("Enter n(1~10): ");
    while(scanf("%d",&n) != EOF){
        float a=1,x=1,s=0,i=1;
        m=n;
        while(n--){
            a=a*i;
            i++;
            s=s+x/a;
            x*=-1;
        }
        printf("n = %d, s = %f\n\n",m,s);
        printf("Enter n(1~10): ");
    }
    
    return 0;
}

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