实验3

#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 main()
{
    int m,k,n;
    k=0;
    for(n=101;n<=200;n++)
    {
        for(m=2;m<=sqrt(n);++m)
         if(n%m==0)break;
        if(m>sqrt(n))
        {
            printf("%d\t",n);
            k++;
            if(k%5==0)
            printf("\n");
            
        }
    }
    printf(" \n");
    printf("101^200之间共有%d个素数",k);
  return 0;
  }

#include<stdio.h>
int main(){
    int s,n,t=0;
    float a=0.1;
    printf("Enter a number:%ld",s);
    scanf("%ld",&s);
    
    while(s>0){
        n=s%10;
        s=s/10;
        if(n%2!=0){
            a=a*10;
            t=n*a+t;
            
        }
    }
    
    printf("new number is:%ld",t);

    return 0;
}

#include <stdio.h>
#include <math.h>
int main(){
    int n, i, factorial = 1;
    double s = 0, sign = 1.00000;
    printf("输入n(1~10):");
    while(scanf("%d",&n) != EOF)
    {   for(i=1;i<=n;i++)
        {
            factorial = factorial * i;
            sign = pow(-1,i+1);
            s = s + sign/factorial;
            continue;
        }
        printf("n = %d  s = %f\n", n, s);
        
        s = 0;
        factorial = 1;
        sign = 1.00000;
        printf("输入n(1~10):");
    }
      return 0;
} 

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