后序非递归遍历打印从根节点到某一结点的路径

这是后序非递归遍历打印从根节点到某一结点的路径
为什么传入一个结点的字符不能运行，而在程序中直接判断字符可以运行
void postorder(BiTree T,char x){
    sqstack S;
    BiTree p=T;
    initstack(S);
    while(p!=NULL||!stackempty(S)){
        while(p!=NULL){
            p->flag=1;
            push(S,p);
            p=p->lchild;
        }
        if(!stackempty(S)){
            pop(S,p);
            if(p->flag==1){
                p->flag=2;
                push(S,p);
                p=p->rchild;
            }
            else{
                visit(p->data);
                if(p->data==x)break;
                p=NULL;        
            }
        }
    }
    destroystack(S);
}

void postorder(BiTree T){
    sqstack S;
    BiTree p=T;
    initstack(S);
    while(p!=NULL||!stackempty(S)){
        while(p!=NULL){
            p->flag=1;
            push(S,p);
            p=p->lchild;
        }
        if(!stackempty(S)){
            pop(S,p);
            if(p->flag==1){
                p->flag=2;
                push(S,p);
                p=p->rchild;
            }
            else{
                visit(p->data);
                if(p->data=='E')break;
                p=NULL;        
            }
        }
    }
    destroystack(S);
}