实验三

实验一
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#define N 5

int main() {
    int x,n;
    
    srand(time(0));
    
    for(n=1; n<=N; n++){
        x = rand() % 100;
        printf("%3d", x);
    }
        printf("\n");
        
        return 0;
} 

　　

实验二
#include<stdio.h>
#include<stdlib.h>
#include<time.h>

int main() {
    int x,n,a; 
    
    srand(time(0));
    x = 1+rand() % 31;
    printf("猜猜2021年5月哪一天是你的lucky day\n开始咯，你有三次机会，猜吧(1~31)");
    for(n=1;n<=3;n++)
	{
	scanf("%d",&a);
	if(a==x)
	{
		printf("恭喜猜对了\n");
		break;
    }
	else if(a<x)
	{
	printf("你猜的日期早了，lucky day还没到呢\n再猜(1~31)"); 
	}
	else 
	{
	printf("你猜的日期晚了，lucky day悄悄溜到前面去啦\n再猜(1~31)");
	}
    }   
	while(n==4)
	{
	printf("次数用完啦，偷偷告诉你，五月，你的luckyday是%d号",x) ;
	break;
	}    

        return 0;

} 

　　

实验三
#include<stdio.h>

int main()
{
   unsigned long x,t,p;
   while(printf("Enter a number:"),scanf("%u",&x)!=EOF){
   
   t=0,p=1;
   while(x!=0){
   
   if((x%10)%2!=0)
   {
   	t=t+(x%10)*p;
   	p=p*10;
   }
   x=x/10;
}
   printf("new number is:%u\n",t);
}
return 0;
}

　　

实验四
#include<stdio.h>
#include<math.h>
void solve(double a, double b, double c);

int main(){
	double a, b, c;
	
	printf("Enter a, b, c:");
	while(scanf("%lf%lf%lf", &a, &b, &c) !=EOF){
		solve(a, b, c);
		printf("Enter a, b, c:");
	}
	return 0;
}


void solve(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));
			x2=(-b-sqrt(delta));
			printf("x1=%.2f,x2=%.f\n",x1,x2);
			
		}
		else{
			real=-b/(2*a);
			imag=sqrt(-delta)/(2*a);
			printf("x1=%.2f+%.2fi,x2=%.2f-%.2fi\n",real, imag,real,imag);
		}
	}
}

否，因为返回值只能有一个，无法将x1,x2同时返回

　　

实验五
#include<stdio.h>
double fun(int n);

int main(){
    int n;
    double s;

    while(printf("Enter n(1~10):"),scanf("%d", &n) != EOF){
        s = fun(n);
        printf("n = %d, s = %f\n\n", n, s);
    }

    return 0;
}
double fun(int n){
	double s=0,x=-1;
	  int i;
	  for(i=1;i<=n;i++){
	  
	    x=-x*1/i;
	    s+=x;
}
      return s;
}

　　

实验六
#include<stdio.h>
#include<math.h>
int isPrime(int n);

int main(){
    int N, n;
    for(n = 101,N = 1;n<200;n++){

        if (isPrime(n))
        {
        printf("%d ", n);
        N++;
         if(N%6 == 0)
         {
         printf("\n");
         N = 1;
         }
        }
    }
    return 0;
}

int isPrime(int n){
    int k;
    for(k=2;k<=sqrt(n);k++)
        if(n%k==0)
        return 0;
        return 1;   
    }