stack.c

#include <stdio.h>
#include <stdlib.h>

typedef struct node {
    int value;
    struct node *next;
} Node;


Node *make_node(int value, Node *next){
    Node *Temp = malloc(sizeof(Node));

    Temp->value = value;
    Temp->next = next;

    return Temp;
}


typedef struct {
    Node *first;
    size_t size;
} Stack;


Stack *make_stack(Node *N){
    Stack *S = malloc(sizeof(Stack));

    S->first = N;
    S->size = (S->first != NULL) ? 1 : 0;

    return S;
}


void stack_push(Stack *S, int value){
    Node *Temp = S->first;

    if(Temp == NULL){
        S->first = make_node(value, NULL);
        S->size++;
        return;
    }

    while(Temp->next != NULL)
        Temp = Temp->next;

    Temp->next = make_node(value, NULL);
    S->size++;
}


void stack_pop(Stack *S){
    Node *Temp = S->first;

    if(Temp == NULL)
        return;

    if(Temp->next == NULL){
        S->first = NULL;
        S->size = 0;
        free(Temp);
        return;
    }

    Node *P;

    while(Temp->next != NULL){
        P = Temp;
        Temp = Temp->next;
    }


    S->size--;
    P->next = NULL;
    free(Temp);
}


Node *stack_top(Stack *S){
    Node *Temp = S->first;

    if(Temp == NULL)
        return NULL;

    while(Temp->next != NULL)
        Temp = Temp->next;

    return Temp;
}


int stack_is_empty(Stack *S){
    return !(S->size > 0 && S->first != NULL);
}


int main(){

    Stack *S = make_stack(NULL);

    for(int i = 1 ; i <= 100; i++)
        stack_push(S, i);

    printf("%d ", stack_top(S)->value);
    printf("\n");

    for(int i = 1 ; i <= 105; i++)
        stack_pop(S);

    printf("Stack is Empty: %d\n", stack_is_empty(S));

    stack_push(S, 123);
    printf("Stack is Empty: %d\n", stack_is_empty(S));

    printf("%d", stack_top(S)->value);

    return 0;

}