本题代码如下

void btreetoexp(tree t, char deep)
{if (t == NULL)return;else if (t->lchild == NULL && t->rchild == NULL)printf("%c", t->data);//输出操作数，不加括号else {if (deep > 1)printf("(");btreetoexp(t->lchild, deep + 1);printf("%c", t->data);btreetoexp(t->rchild, deep + 1);if (deep > 1)printf(")");}
}

完整测试代码

#include<stdio.h>
#include<stdlib.h>
typedef struct treenode {char data;struct treenode* lchild, * rchild;
}treenode, * tree;
void buildtree(tree* t)//建树
{char ch;ch = getchar();if (ch == '#')*t = NULL;else{*t = (treenode*)malloc(sizeof(treenode));//分配空间(*t)->data = ch;(*t)->lchild = NULL;(*t)->rchild = NULL;buildtree(&((*t)->lchild));buildtree(&((*t)->rchild));}
}
void btreetoexp(tree t, char deep)
{if (t == NULL)return;else if (t->lchild == NULL && t->rchild == NULL)printf("%c", t->data);//输出操作数，不加括号else {if (deep > 1)printf("(");btreetoexp(t->lchild, deep + 1);printf("%c", t->data);btreetoexp(t->rchild, deep + 1);if (deep > 1)printf(")");}
}
int main() {tree t;buildtree(&t);btreetoexp(t, 1);//根的高度为1return 0;
}
//*+a##b##*c##-#d##
/**+		*
a	  b   c    -d*/