C++ Program to Implement Expression Tree Algorithm

An expression tree is basically a binary which is used to represent expressions. In expression tree, internal nodes correspond to operators and each leaf node corresponds to an operand. Here is a C++ Program to implement the Expression Tree Algorithm which takes the postfix expression as an input and generates the corresponding expression tree traversed in inorder.

Algorithm

Begin    function construct_expression_tree():       Flag = 1 when it is operand.       Flag = -1 when it is operator.       S = suffix[0] means read the first operand from the expression.    For i = 0 and until s != 0       Check symbol is operand or operator.       Call function void inorder() for inorder traversal.       Print the results.       Increment i End.

Example Code

#include <iostream> using namespace std; struct n//node declaration {    char d;    n *l;    n *r; }; char pf[50]; int top = -1; n *a[50]; int r(char inputch)//check the symbol whether it is an operator or an operand. {    if (inputch == '+' || inputch == '-' || inputch == '*' || inputch == '/')       return (-1);    else if (inputch >= 'A' || inputch <= 'Z')       return (1);    else if (inputch >= 'a' || inputch <= 'z')       return (1);    else       return (-100); } void push(n *tree)//push elements in stack {    top++;    a[top] = tree; } n *pop() {    top--;    return (a[top + 1]); } void construct_expression_tree(char *suffix) {    char s;    n *newl, *p1, *p2;    int flag;    s = suffix[0];    for (int i = 1; s!= 0; i++) {       flag = r(s);       if (flag == 1) {          newl = new n;          newl->d = s;          newl->l = NULL;          newl->r = NULL;          push(newl);       } else {          p1 = pop();          p2 = pop();          newl = new n;          newl->d = s;          newl->l = p2;          newl->r = p1;          push(newl);       }       s = suffix[i];    } } void inOrder(n *tree)//perform inorder traversal {    if (tree != NULL) {       inOrder(tree->l);       cout << tree->d;       inOrder(tree->r);    } } int main(int argc, char **argv) {    cout << "Enter Postfix Expression : ";    cin >>pf;    construct_expression_tree(pf);    cout << "\nInfix Expression : ";    inOrder(a[0]);    return 0; }

Output

Enter Postfix Expression : 762*+6+ Infix Expression : 7+6*2+6