Implementation of stack using linked list - c

Question

I am getting a "Function should return a value" error at the 91st line of the code in Turbo C++, please help me as I have to submit my project, I know that Turbo C++ is a very old compiler but that's what our University Teacher recommends so I cant do nothing in that
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#include <stdio.h>
#include <conio.h>
struct stack
{
int element;
struct stack *next;
} * top;
void push(int);
int pop();
void display();
void main()
{
int num1, num2, choice;
while (1)
{
clrscr();
printf("Select a choice from the following:");
printf("\n[1] Push an element into the stack");
printf("\n[2] Pop out an element from the stack");
printf("\n[3] Display the stack elements");
printf("\n[4] Exit\n");
printf("\n\tYour choice: ");
scanf("%d", &choice);
switch (choice)
{
case 1:
{
printf("\n\tEnter the element to be pushed into the stack: ");
scanf("%d", &num1);
push(num1);
break;
}
case 2:
{
num2 = pop();
printf("\n\t%d element popped out of the stack\n\t", num2);
getch();
break;
}
case 3:
{
display();
getch();
break;
}
case 4:
exit(1);
break;
default:
printf("\nInvalid choice !\n");
break;
}
}
}
void push(int value)
{
struct stack *ptr;
ptr = (struct stack *)malloc(sizeof(struct stack));
ptr->element = value;
ptr->next = top;
top = ptr;
return;
}
int pop()
{
if (top == NULL)
{
printf("\n\STACK is Empty.");
getch();
exit(1);
}
else
{
int temp = top->element;
top = top->next;
return (temp);
}
}
void display()
{
struct stack *ptr1 = NULL;
ptr1 = top;
printf("\nThe various stack elements are:\n");
while (ptr1 != NULL)
{
printf("%d\t", ptr1->element);
ptr1 = ptr1->next;
}
}
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Answer 1

The compiler is complaining because you don’t have a return statement outside of the if statement. Even though you call exit in the if branch, syntactically speaking that’s just another function call; structurally, the compiler sees a pathway where you reach the closing } of the function body without a return statement.
You want to make sure the return is reachable outside the body of the if-else statement, and the best way to do it is take the else branch out of the statement entirely:
int pop( void )
{
int temp;
if ( !top )
{
fputs( "Stack is empty", stderr );
exit( 1 );
}
temp = top->element;
top = top->next;
return temp;
}

Answer 2

you can change your pop function as below ( assuming you are not storing -1 as an element in the stack)
int pop()
{
if (top == NULL)
{
printf("\n\STACK is Empty.");
getch();
return -1;// or other invalid value which indicates stack empty
}
else
{
int temp = top->element;
top = top->next;
return (temp);
}
}
and at the place you are calling modify as following
case 2:
{
num2 = pop();
if(num2 != -1) {
printf("\n\t%d element popped out of the stack\n\t", num2);
getch();
}else{
printf("Stack is Empty\n");
exit(1);
}
break;
}