实验三

#include <stdio.h>
#include <math.h> 
#include<stdlib.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<stdlib.h>
int main()
{
    int i,j,sum=0;
    for(i = 101 ; i <= 200 ; i++ )
    {
        for(j = 2 ; j < i ; j++)
        {
            if(i % j == 0)          
            {
                break;
            }
            else
            {
                if( j == i-1 )          
                {
                    printf("%d ",i);
                    system("color 35");
                    sum++;
                }
            }
        
          }
    }
    printf("\n");
    printf("100~200之间共有%d个素数。",sum);
    return 0;
}

#include<stdio.h>
 #include<string.h>
int main(){
    char number[50]={0};
    while(printf("Enter a number:"),scanf("%s",number)!=EOF)
    {
    int len=strlen(number);
    printf("new number is:");
    for(int i=0;i<len;i++){
        if((number[i]-'0')%2!=0){
            printf("%c",number[i]);
        }
    }
    
    printf("\n\n");
}
    return 0;
}

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

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main(){
    int x=0,n=0;
    srand(time(0));
    while(x==0){
    x=rand()%31;
    }
    for(int i=0;i<3;i++){
        scanf("%d",&n);
        if(n==x){
            printf("你居然猜中了，有意思！");
            break;
        }
        if(n<x){
            printf("太早了啊");
        }
        if(n>x){
            printf("好迟啊");
        }
        printf("\n");
        if(i==2){
            printf("哈哈，告诉你吧这个数是%d!",x);
        }
    }
    return 0;
}

总结：得到很多有意思的发现，解决了部分之前的疑点；也用到了上次兄弟给的建议，但为了不影响原样，只给出结果，代码未随意改变。