Prefix to Postfix Conversion using Stack Data Structure (With C++ Program Code)
In this tutorial we will convert in Prefix Expression to a Postfix Expression using Stack Data structure. We will understand the Rules to convert a Prefix expression to Postfix expression and also understand the pseudocode. Lastly we will write a C++ program to perform Prefix to Postfix expression conversion.
Rules for Prefix to Postfix using stack DS –
- Scan PREFIX expression from RIGHT to LEFT
- IF the incoming symbol is a OPERAND, PUSH it onto the Stack
- IF the incoming symbol is a OPERATOR, POP 2 OPERANDs from the Stack, ADD this incoming OPERATOR in before the 2 OPERANDs & PUSH this whole new expression string back into the Stack.
- At the end POP and PRINT the full POSTFIX expression from the Stack.
PSEUDOCODE –
C++ Program to Postfix to Prefix Conversion using Stack DS –
#include<iostream> #include<stack> using namespace std; bool isOperand(char c) { if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')) { return true; } else { return false; } } string PrefixToPostfix(string prefix) { stack < string > s; for (int i = prefix.length() - 1; i >= 0; i--) { if (isOperand(prefix[i])) { string op(1, prefix[i]); s.push(op); } else { string op1 = s.top(); s.pop(); string op2 = s.top(); s.pop(); s.push(op1 + op2 + prefix[i]); } } return s.top(); } int main() { string prefix, postfix; cout << "Enter a PREFIX Expression :" << endl; cin >> prefix; cout << "PREFIX EXPRESSION: " << prefix << endl; postfix = PrefixToPostfix(prefix); cout << endl << "POSTFIX EXPRESSION: " << postfix; return 0; }