实验3

// 一元二次方程求解
//ctrl+z结束
#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;
} 

// 生成N个0~9之间的随机整数， 并打印输出
#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 ;
} 

//3
#include <stdio.h>
#include <math.h> 
int main() {
    int n,i,m,N=0;
    for(n=101;n<=200;n++)
    {
    m=sqrt(n);
    
    for(i=2;i<=m;i++)
    {
    
      if(n%i==0)break;
      if(i==m){
      
       printf("%6d",n);
       N++;
}   
}
}
   printf("\n101~200之间共有%d个素数，\n",N);
   return 0 ;
}

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

#include <stdio.h>
int main(){
    int n;
    printf("Enter n(1~10): ");
    while(scanf("%d", &n)!=EOF){
        int t, f, T;
        f = 1; T = 1;
        double s = 0.0;
        for (t = 1;t <= n; t++){
            T = t * T;
            s = s + f * (1.0 / T);
            f = f * (-1);
        }
        printf("n = %d, s = %f\n\n", n, s);
        printf("Enter n (1~10): ");
    }
}

#include <stdio.h>
#include <time.h>
#include <stdlib.h>
int main(){
    int x,i,date = 6;
    srand((unsigned)time(NULL));
    x = rand()%31 + 1;
    printf("猜猜2020年12月哪一天会是你的lucky day\n");
    printf("开始喽，你有三次机会，猜吧(1~31): ");
    for(i = 1;i <= 3;i++)
       { scanf("%d",&x);
          if(x > date)
          {printf("\n你猜的日期晚了，lucky day悄悄溜到前面啦\n"); }
 
           else if(x < date)
           {printf("\n你猜的日期早了，lucky day还没到呢\n");}
           if(i != 3){ printf("\n再猜(1~31): ");}
        }
 
        printf("次数用完啦，偷偷告诉你：12月，你的lucky day是6号");
        return 0;
        }

通过本次实验，充分认识到了理论和实践的差距，一定要好好实践啊！！！！