实验3

#include<stdio.h>
#include<stdlib.h>
#define N 5

int main(){
    
    int x,n;
    
    srand(time(0));//time 返回一个值，是格林尼治时间1900年1月1日距现在的秒数（可保证不同的数） 
    
    for(n=1;n<=N;n++){
        
        x=1+rand()%30;//rand,取time前的任一个数 ;31即可取0~31的随机数 
        
        printf("%3d",x);
    }
    
    printf("\n");
    
    
    return 0;
    
    
} 

#include<stdio.h>
#include<stdlib.h>
int rad();  
int main(){
    int x=3,i,y,ans;
    printf("Guess which day is your lucky day!\n");
    printf("Begins! You have %d chances,let us guess!(1~31)",x);
    
    y=rad();
    
    for(i=1;i<=x;i++)
    {

        
        scanf("%d",&ans);
        
        if(ans==y)
          {
          printf("Yep!U R right!\n");
          exit(0);
          }
        else if(ans>y)
          {
           printf("oH~ U R wrong!The right one is in front of your ans!\n");
                   printf("Guess it again!(1~31)");
          }
        else
          {
           printf("oH~ U R wrong!The right one is behind your ans!\n");
                  printf("Guess it again!(1~31)");
         }
          
    }
    printf("oh,no~Your chances are used off!Let me tell you: it is %d!\n",y);
    
    return 0;
    
    
} 
int rad(){
    int x;
    srand(time(0));
    x=1+rand()%30;
    return x;
}

#include<stdio.h>
#include<math.h>
int main(){
    long outcome,x,number;
    int y,count,m;

    printf("Enter a number:");
    
    while(scanf("%ld",&number)){
        count=1;
        outcome=0;
    for(;number!=0;)
    {

        x=number%10;
              
        if(x%2!=0)
        { 
           m=1;
            for(y=1;y<count;y++)
            {
                
                m*=10;
            }
            
            outcome+=x*m;
               count++;
        }
        number/=10;
    }
    printf("\nnew number is:%ld\n\n",outcome);
    printf("Enter a number:");
    
}

    
    return 0;
}

#include <math.h> 
#include <stdio.h>
double solve1(double a, double b, double c);
double solve2(double a, double b, double c);
int main() 
{ 
    double a, b, c,x1,x2;
    
    printf("Enter a, b, c: "); 
    while(scanf("%lf%lf%lf", &a, &b, &c) != EOF) 
    {
        x1= solve1(a, b, c);
        x2= solve2(a,b,c);
        printf("x1=%f,x2=%f\n",x1,x2); 
        printf("Enter a, b, c: ");
    }
    
     return 0;
}




double solve1(double a, double b, double c) { 
           double x1, x2; 
           double delta, real, imag;
           
           
    if(a == 0) 
        printf("not quadratic equation.\n"); 
    else {
        delta = b*b - 4*a*c;
                
    if(delta >= 0) { 
                  x1 = (-b + sqrt(delta)) / (2*a);
                  x2 = (-b - sqrt(delta)) / (2*a); 
                  return x1;
                  } 
                  
    else {
            real = -b/(2*a); 
            imag = sqrt(-delta) / (2*a); 
            printf("x1 = %.2f + %.2fi, x2 = %.2f - %.2fi\n", real, imag, real, imag);
          exit(0);         
        }
     }
   }



double solve2(double a, double b, double c) { 
           double x1, x2; 
           double delta, real, imag;
           
           
    if(a == 0) 
        printf("not quadratic equation.\n"); 
    else {
        delta = b*b - 4*a*c;
                
    if(delta >= 0) { 
                  x1 = (-b + sqrt(delta)) / (2*a);
                  x2 = (-b - sqrt(delta)) / (2*a); 
                  return x2;
                  } 
                  
    else {
            real = -b/(2*a); 
            imag = sqrt(-delta) / (2*a); 
            printf("x1 = %.2f + %.2fi, x2 = %.2f - %.2fi\n", real, imag, real, imag);
            exit(0);             
        }
      }
   }

task5
#include <stdio.h> 
double fun(int n);  
int main() { 
    int n;
    double s; 
    
    printf("Enter n(1~10): "); 
    
    while(scanf("%d", &n) != EOF) { 
     
     s = fun(n);  
     printf("n = %d, s= %f\n\n", n, s); 
     printf("Enter n(1~10): "); 
    
     }

return 0; 

}

double fun(int n){
    int i,j,a,sign;
    double part,ans;
    
   
    sign=1;
    ans=0.0;

   for(i=1;i<=n;i++)
   {
       a=1;
          for(j=1;j<=i;j++)
          {
                 a*=j;
          }
          
        part=sign*((double)1.0/a);
        sign=(-1)*sign;
          
         ans+=part;
    }
    
    return ans;
}

#include<stdio.h>
#include<math.h>
int isprime(int n);//insert 可改成插入或者覆盖模式 
int main()
{
    
    int i;
    int count=0;
    
    for(i=101;i<=200;i++)
    {
        
        if(isprime(i))
        {
            
            if(count%5==0&&count!=0)
            {
                printf("\n");
            }
            
            printf("%4d",i);//不知道为什么输出前面会有一个空格 
            count++;
        }
           
    }
    printf("\n 100~200的素数个数为%d",count);
    return 0;    
}
int isprime(int n){
    int k;
    
    for(k=2;k<=sqrt(n);k++)
       if(n%k==0)
          return 0;
        return 1;
        
}