Variable undeclared in function

Question

Hi I'm having a problem with global pointer being underclared in function. Here is my code

#include <iostream>

using namespace std;

void push_l(int n);


struct elem{ 
       int key; 
       elem *next;
} *left=NULL,*right=NULL;
void push_l(int n){
     elem *p=left;
     left=new elem;
     left->key=n;
     left->next=p;
     if (right==NULL)right=left;
} 

int main(){
  push_l(5);
  system "pause";
  return 0;
}

This is one of the error messages I get - In function void push_l(int) left underclared

Answer 1

This is what you get for using namespace std; (std has a left too). And you don't even need iostream. The reference to left is ambiguous.

Do this:

#include <cstdlib>    

struct elem{ 
       int key; 
       elem *next;
} *left=NULL,*right=NULL;

void push_l(int n){
     elem *p=left;
     left=new elem;
     left->key=n;
     left->next=p;
     if (right==NULL)right=left;
} 

int main(){
  push_l(5);
  std::system("pause");
  return 0;
}