construct expression tree

/*
Given a postfix expression.Your task is to complete the method constructTree().The output of the program will print the infix expression of
the given postfix expression.

Input:
The constructTree() function takes a single argument as input,character array containg the given postfix expression.
Output:
Infix expression should be printed for each given postfix expression.
Constraints:
1<=T<=50
1<=length_of_expression<=20
Example:
Input:
2
ab+ef*g*-
wlrb+-*
Output:
a + b - e * f * g
w * l - r + b
*/

et* constructTree(char postfix[])
{
stack<et *> st; 
    et *t, *t1, *t2; 
  
    
    for (int i=0; i<strlen(postfix); i++) 
    { 
        if (!isOperator(postfix[i])) 
        { 
            t = newNode(postfix[i]); 
            st.push(t); 
        } 
        else  
        { 
            t = newNode(postfix[i]); 
  
            t1 = st.top(); 
            st.pop();       
            t2 = st.top(); 
            st.pop(); 
  
            
            t->right = t1; 
            t->left = t2; 
  
            st.push(t); 
        } 
    } 
    t = st.top(); 
    st.pop(); 
  
    return t; 
}