binary threading tree

/* Binary threading tree can be used where frequent searching are needed. * Because there is no recursive function and the codes run quite efficiently. */#include "/usr/c/head.h"typedef char elemtype;typedef enum {link, thread} pointertag;typedef struct bitreenode {elemtype data;struct bitreenode * lchild, * rchild;pointertag ltag, rtag;}bitreenode, * bitree;bitree pre;status creat_tree(bitree * T) {elemtype ch;int temp;printf("Input element:");SCAN_CHAR(ch, temp);if (ch == ' ')*T = NULL;else {*T = (bitree)malloc(sizeof(bitreenode));if (!(*T)) exit(OVERFLOW);(*T)->data = ch;creat_tree(&(*T)->lchild);creat_tree(&(*T)->rchild);if ((*T)->lchild)(*T)->ltag = link;else (*T)->ltag = thread;if ((*T)->rchild)(*T)->rtag = link;else(*T)->rtag = thread;}return OK;}status visit(bitree p) {printf("%c/tltag = %d. rtag = %d./n", p->data, p->ltag, p->rtag);return OK;}status in_order_traverse(bitree T) {if (T) {in_order_traverse(T->lchild);visit(T);in_order_traverse(T->rchild);}return OK;}status inthreading(bitree p) {if (p) {inthreading(p->lchild);if (!p->lchild)p->lchild = pre;if (!pre->rchild)pre->rchild = p;pre = p;inthreading(p->rchild);}return OK;}status in_order_threading(bitree * thrt, bitree T) {*thrt = (bitree)malloc(sizeof(bitreenode));if (!(*thrt)) exit(OVERFLOW);(*thrt)->ltag = link;(*thrt)->rtag = thread;(*thrt)->rchild = *thrt;if (!T)(*thrt)->lchild = *thrt;else {(*thrt)->lchild = T;pre = *thrt;inthreading(T);pre->rtag = thread;pre->rchild = *thrt;(*thrt)->rchild = pre;}return OK;}status in_order_traverse_thrt(bitree thrt) {bitree p;p = thrt->lchild;while (p != thrt) {while (p->ltag == link)p = p->lchild;visit(p);while (p->rtag == thread && p->rchild != thrt) { /* Be carefull here, if "p->rchild != thrt" is missed, the function will step into endless loop.*/p = p->rchild;visit(p);}p = p->rchild;}return OK;}int main(void) {bitree T;bitree thrt;creat_tree(&T);printf("In_order_traverse:/n");in_order_traverse(T);in_order_threading(&thrt, T);printf("In_order_traverse_thrt:/n---------------------------/n");;in_order_traverse_thrt(thrt);return 0;}