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C++ Program to Construct an Expression Tree for a Postfix Expression
An expression tree is basically a binary tree which is used to represent expressions. In expression tree, nodes correspond to the operator and each leaf node corresponds to the operand. This is a C++ program to construct an expression tree for a postfix Expression in inorder, preorder and postorder traversals.
Algorithm
Begin Function r() has a character variable as parameter. If the characters are + or - or * or / then Return will be -1 If the characters are from A to Z then Return will be 1. If the characters are from a to z then Return will be 1. Else Return -100. Function construct_expression_tree() to construct the expression tree Function push() to push values in the stack Function pop() to pop values from the stack Function preOrder() for pre-order traversal Function inOrder() for in-order traversal Function postOrder() for post-order traversal End.
Example Code
#include <iostream>
using namespace std;
struct n {
char d;
n *l;
n *r;
};
char pf[50];
int top = -1;
n *a[50];
int r(char inputch) {
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) {
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 preOrder(n *tree) {
if (tree != NULL) {
cout << tree->d;
preOrder(tree->l);
preOrder(tree->r);
}
}
void inOrder(n *tree) {
if (tree != NULL) {
inOrder(tree->l);
cout << tree->d;
inOrder(tree->r);
}
}
void postOrder(n *tree) {
if (tree != NULL) {
postOrder(tree->l);
postOrder(tree->r);
cout << tree->d;
}
}
int main(int argc, char **argv) {
cout << "Enter Postfix Expression : ";
cin >> pf;
construct_expression_tree(pf);
cout << "\nIn-Order Traversal : ";
inOrder(a[0]);
cout << "\nPre-Order Traversal : ";
preOrder(a[0]);
cout << "\nPost-Order Traversal : ";
postOrder(a[0]);
return 0;
}Output
Enter Postfix Expression : 762*+6+ In-Order Traversal : 7+6*2+6 Pre-Order Traversal : ++7*626 Post-Order Traversal : 762*+6+
Updated on: 30-Jul-2019
2K+ Views
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