Question

C++中编写的程序运行时提示内存为只读 大侠们帮我看看嘛，谢谢

#include<iostream.h>
#include<string.h>
#include<math.h>
struct node
{
char city[5];
float x;
float y;
node * next;
};
struct list
{
node * head;
};
void add(list &L)
{
node *s,*r;
int i;
for(i=1;i<=4;i++)
{
L.head=NULL;
s=new node;
cout<<"city:";
cin>>s->city;
cout<<"x:";
cin>>s->x;
cout<<"y:";
cin>>s->y;

if(L.head==NULL)
{
L.head=s;
r=s;
}
else
{
r->next=s;
r=s;
}
}
}
void find1(list &L)
{
node *p;
char a[5];
cout<<"请输入查找的城市名：";
cin>>a;
cout<<"x y"<<endl;
p=L.head;
while(p!=NULL)
{
if((strcmp(p->city,a))==0)
{
cout<<p->x<<" "<<p->y<<endl;
}
p=p->next;
}
}
void find2(list &L)
{
float a,b,c;
node *p;
cout<<"请给定一个位置坐标：";
cin>>a>>b;
cout<<"请给定一个距离：";
cin>>c;
p=L.head;
cout<<"city"<<endl;
while(p!=NULL)
{
if((((p->x)-a)*((p->x)-a)+((p->y)-b)*((p->y)-b))<=c)
{
cout<<p->city<<endl;
}
p=p->next;
}
}
void main()
{
list L;
add(L);
find1(L);
find2(L);
}

Answer 1

for(i=1;i<=4;i++)
{
L.head=NULL;
//这里，你每次循环赋值都将链表头置空？？
L.head=NULL; 这条语句挪到main函数add(L);之前。

Answer 2

你好，add函数定义有问题，修改如下：

void add(list &L)
{
	node *s,*r;
	int i;
	L.head=NULL;
	for(i=1;i<=4;i++)
	{
		s=new node;
		cout<<"city:";
		cin>>s->city;
		cout<<"x:";
		cin>>s->x;
		cout<<"y:";
		cin>>s->y;

		if(L.head==NULL)
		{
			L.head=s;
			r=s;
		}
		else 
		{
			r->next=s;
			r=s;
		}
	}

	r->next=NULL;    //要赋空，否则后面的判断是会出问题的
	r=s;
}

若有疑问，请追问，满意请采纳

Answer 3

void add(list &L)
{
node *s,*r;
//r=new node;//加一句这个试试，反正我加了以后没出问题
int i;
for(i=1;i<=4;i++)
{
L.head=NULL;
s=new node;
cout<<"city:";
cin>>s->city;
cout<<"x:";
cin>>s->x;
cout<<"y:";
cin>>s->y;
if(L.head==NULL)
{
L.head=s;
r=s;
}
else
{
r->next=s;
r=s;
}
}
}