How to evaluate binary tree (inorder)? - c

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;