Hello, I made a code that uses a double connection list to input Corona information by country and print it out, but there are dozens of compilation errors I don't know what the problem is Attached is the code
#include <iostream>
#include <string>
using namespace std;
Node* g_head = NULL;
Node* g_tail = NULL;
int g_count = 0;
class Node {
public:
string m_nation = "";
int m_occur = 0;
int m_deadman = 0;
double m_mortality = 0;
Node* next = NULL;
Node* prev = NULL;
Node(string nation = "", int occur = 0, int deadman = 0, Node* left = NULL){
m_nation = nation;
m_occur = occur;
m_deadman = deadman;
m_mortality = deadman / occur;
if (g_count == 0) {
g_head = this;
g_tail = this;
g_count++;
}
else {
g_tail = this;
prev = left;
prev->next = this;
g_count++;
}
}
private:
protected:
};
void print_all_list() {
Node* pt = g_head;
for (int i = 0; i < g_count; i++) {
cout << pt->m_nation << " " << pt->m_occur << " " << pt->m_deadman << " " << pt->m_mortality << endl;
pt = pt->next;
}
}
int main(void) {
Node America("America", 43214, 533);
Node China("China", 81711, 3277,&America);
Node France("France", 19856, 869, &China);
Node Germany("Germany", 29056, 123, &France);
Node Iran("Iran", 23049, 1812, &Germany);
Node Italy("Italy", 63927, 6077, &Iran);
Node Korea("Korea", 9037, 120, &Italy);
Node Spain("Spain", 33098, 2182, &Korea);
print_all_list();
return 0;
}
There is a compilation error like below.
/solution0.cpp:5:1: error: unknown type name 'Node'
Node* g_head = NULL;
^
/solution0.cpp:6:1: error: unknown type name 'Node'
Node* g_tail = NULL;
To use a type name in C++, it must already be declared.
Node*g_head = NULL; is above the definition of classNode.
In other words, Node does not exist at the time g_head is declared.
To resolve this issue, you must either use a forward declaration or move g_head and g_tail to the lower line of the Node definition.
However, the Node constructor uses two global variables, so I'll make a forward declaration.
Change to classNode*g_head = NULL; and classNode*g_tail = NULL;.
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