Non-recursive traversal implementation of binary tree sequence, middle sequence and sequential order (C language)

First , non-recursive sequential traversal

void Treversepreorder (struct btree *t)
{struct btree
    ;
    int top=0;
    while (p| | Top)
    {
        if (p)
        {
            printf ("%d", p->data);
            stack[top++]=p;
            p=p->left;
        }
        else
        {
            p=stack[--top];
            p=p->right;}}}

second, non-recursive sequence traversal

void Treverseinorder (struct btree *t)
{struct btree
    ;
    int top=0;
    while (p| | Top)
    {
        if (p)
        {
            stack[top++]=p;
            p=p->left;
        }
        else
        {
            p=stack[--top];
            printf ("%d", p->data);
            p=p->right;}}}

third, non-recursive subsequent traversal

void treversepostorder (struct btree *t) {struct btree;
    int top=0; while (p| |
            Top) {if (p) {stack[top++]=p;
        p=p->left;
            } else {p=stack[top-1];
                if (p->right&&p->right!=r)//Right subtree, not empty and not accessed, you need to traverse {p=p->right;
            stack[top++]=p;//Current Right sub-tree pressure stack p=p->left;
                else//the right subtree is empty, direct access to {P=stack[--top];
                printf ("%d", p->data);
            R=P;//R Save node P=null; }
        }
    }
}