如何评估二叉树（顺序）？

Question

I am trying to evaluate a binary tree (inorder). The result always remains the same or giving an unexpected answer. I do not know where the problem is, can anyone help me? First I have converted postfix expression to expression tree than evaluate expression tree. I shall be very thankful.

The result is unexpected when I run this program. This the header file.

#define POST2EXPTREE_H_INCLUDED
#define MAX 100

struct node
{
    char ch;
    struct node *left;
    struct node *right;
}  *stack[MAX];
typedef struct node node;
void push(node *str);
node *pop();
void convert(char exp[]);
void display(node *temp);

#endif

#include <stdio.h>
#include <stdlib.h>
#include"post2expTree.h"
#define SIZE 100

int top = -1;
void push(node *str)
{
    if (top >= MAX-1)
    printf("Stack is Full ");
    else
    {
        stack[top] = str;
        top++;
    }
}

node *pop()
{
    node *exp;
    if (top < 0)
        printf("Stack is Empty ");
    else
        exp = stack[--top];
    return exp;
}
void convert(char exp[])
{
    node *op1,  *op2;
    node *temp;
    int i;
    for (i=0;exp[i]!='\0';i++)
    if (exp[i] >= 'a'&& exp[i] <= 'z'|| exp[i] >= 'A' && exp[i] <= 'Z' ||isalnum(exp[i]))
    {
        temp = (node*)malloc(sizeof(node));
        temp->ch = exp[i];
        temp->right = NULL;
        temp->left = NULL;
        push(temp);
    }
    else if (exp[i] == '+' || exp[i] == '-' || exp[i] == '*' || exp[i] == '/' || exp[i] == '%'
|| exp[i] == '^')
    {
        op1 = pop();
        op2 = pop();
        temp = (node*)malloc(sizeof(node));
        temp->ch = exp[i];
        temp->right = op1;
        temp->left = op2;
        push(temp);
    }
}

void display(node *temp)
{
    if (temp != NULL)
    {
        display(temp->left);
        printf("%c", temp->ch);
        display(temp->right);
    }
}
int evaluate(node *temp)
{
    int left,right,value;
    if ((temp->ch) >= 0 || (temp->ch <=9))
    {
        return temp->ch;
    }
    else
    {
        left = evaluate(temp -> left);
        right = evaluate(temp -> right);

        switch(temp->ch)

        {

            case '+':
                value = left + right;
                break;

            case '-':
                 value = left - right;
                 break;


            case '*':
                 value = left * right;
                break;


            case '/':
                 value = left / right;
                break;


            case '%':
                 value = left % right;
                break;


            case '^':
                 value = left ^ right;
                break;


        }
        temp->ch = value;
    }
    return value;

}

Answer 1

  int top = -1; void push(node *str) { if (top >= MAX-1) printf("Stack is Full "); else { stack[top] = str; top++; } } 

• Here top is initialized to -1 , and the very first push() wrongly accesses stack[-1] ; correct that by changing the else block to stack[++top] = str; .

  node *pop() { node *exp; if (top < 0) printf("Stack is Empty "); else exp = stack[--top]; return exp; } 

• Here top is decremented before accessing the stack off by one; correct that by changing the else block to exp = stack[top--]; .

  int evaluate(node *temp) { int left,right,value; if ((temp->ch) >= 0 || (temp->ch <=9)) { return temp->ch; 

• Here you forgot that you store the operands as single digits '0' to '9' , not as values 0 to 9 . Correct that by changing to:

    int left, right, value = temp->ch-'0'; if (value >= 0 && value <= 9) { return value;