http://pythontutor.com/

visualize stack

#include <stdlib.h>
#include <stdio.h>
struct NODE{
    int data;
    struct NODE *link;
};
struct STACK{
    int count;
    struct NODE *top;
};
bool is_empty(struct STACK *s){
    if (s->count == 0) {
        return true;
    }
    return false;
}

void push(struct STACK *s, int score){
    struct NODE *pnew =  (struct NODE*)malloc(sizeof(struct NODE)); //new NODE;
    pnew->data = score;
    if (is_empty(s)) {
        pnew->link = NULL;
    }
    else{
        pnew->link = s->top;
    }
    s->count++;
    s->top = pnew;
}

int pop(struct STACK *s){
    if (!is_empty(s)) {
        int data = s->top->data;
        struct NODE *old = s->top;
        s->top = s->top->link;
        s->count--;
        free(old);
        return data;
    }
    return NULL;
}
int main(){
    struct STACK s1, s2;
    s1.count=0;
    s2.count=0;
    push(&s1, 88);
    push(&s1, 60);
    push(&s1, 37);
    push(&s1, 50);
    for (int i=0; i<4; i++) {
        int data = pop(&s1);
        printf("stack1 - %d : %d\n", i, data);
        push(&s2, data);
    }
    printf("\n");
    for (int i=0; i<4; i++) {
        printf("stack2 - %d : %d\n", i, pop(&s2));
    }
    printf("\n");
}