linked list not printing correctly? - c++

Question

struct stack_struct
{
int number;
struct stack_struct *next_number;
};
stack_struct *mainStruct;
class stack_class
{
private:
struct stack_struct *head;
public:
stack_class();
//~stack_class();
void pushNumber(int number);
void popANumber();
void findNumber();
void clearStack();
void sizeFinder();
void printStack();
};
stack_struct *pointerFunc,*pointerFunc2,*pointerFunc3,*printPointer;
stack_class::stack_class()
{
head=NULL;
}
void stack_class::pushNumber(int numberFunc)
{
if(head==NULL)
{
head = new stack_struct;
head->number = numberFunc;
head->next_number = NULL;
pointerFunc2=head;
}
else
{
pointerFunc = new stack_struct;
pointerFunc->number=numberFunc;
pointerFunc->next_number=NULL;
head->next_number=pointerFunc;
head=pointerFunc;
}
}
void stack_class::printStack()
{
while(pointerFunc2)
{
cout<<pointerFunc2->number<<endl;
pointerFunc2=pointerFunc2->next_number;
}
}
int optionChosen;
int main()
{
stack_class mainClassStack;
do
{
cin>>optionChosen;
switch(optionChosen)
{
case 1:
{
int pushInt;
cout<<"\n\nEnter Number: ";
cin >> pushInt;
mainClassStack.pushNumber(pushInt);
break;
}
case 2:
{
break;
}
case 3:
{
break;
}
case 4:
{
break;
}
case 5:
{
break;
}
case 6://print
{
mainClassStack.printStack();
break;
}
default:
{
break;
}
}
}while(optionChosen!=7);
return 0;
I am trying to implement a stack type of data list using dynamic memory (linked list). But when I try to prints the list, it only prints the list once, and if I try to reprint again using option 6, its like the list is gone. I went over the code twice but couldnt figure out what the problem was. Any suggestions?

Answer 1

The problem with your code is that after you print the stack, you aren't resetting pointerFunc2 to become head.
Either reset it correctly, or use a local variable inside your print function.
Here's a corrected version of your function:
void stack_class::printStack()
{
while (pointerFunc2)
{
cout << pointerFunc2->number << endl;
pointerFunc2 = pointerFunc2->next_number;
}
// reset pointerFunc2 so the next iteration
// can start at the head and print again.
pointerFunc2 = head;
}

Answer 2

The problem is when you print the stack the first time with this
pointerFunc2=pointerFunc2->next_number;
the pointerFunc2 becomes the last element after the first iteration. So that's why you think its gone. You should reset pointerFunc2 to point to the head node after being printed. So save it first, then after iterating thru the whole list, restore it, so that the next time you print the stack you will start with the head node.

Answer 3

The reason the second print does not work is that you are using a global variable instead of a local one:
stack_struct *pointerFunc2;
When you declare a variable outside a function or a class, it becomes global variable. Global variables survive function invocations, and retain the value that was last set into them. In order to be local, a variable needs to be declared inside printStack, initialized to the stack's head, and then discarded upon exiting the function. The same is true about pointerFunc.
The printPointer and pointerFunc3 variables are unused, and can be removed from the source code.