# Conversion of Prefix to Postfix notation ### Problem statement

Given an arithmetic expression in prefix notation , convert it into the equivalent postfix notation.

Sample example :

Prefix input: *ab

Postfix output : ab*

### Introduction to Arithmetic Notations

Any arithmetic expression consists of operands and operators . The way we arrange our operators and operands to write the arithmetic expression is called Notation .

There are three different notations for writing the Arithmetic expression :

• Infix expression An expression is said to be in infix notation if the operators in the expression are placed in between the operands on which the operator works.
For example => a + b * c Infix expressions are easy to read ,write and understand by humans , but not by computer It’s costly , in terms of time and space , to process Infix expressions

• Postfix expression (Reverse Polish Notation) An expression is said to be in postfix notation if the operators in the expression are placed after the operands on which the operator works. For example => abc*+ It’s most used to notation for evaluating arithmetic expression

• Prefix expression (or Polish Notation ) An expression is said to be in prefix notation if the operators in the expression are placed before the operands on which the operator works. For example => +a*bc

### Precedence order and Associativity of Operators

In this article we are gonna talk about how to convert prefix expression into postfix expression For the simplicity and understanding purpose , we will consider only ‘+’ , ‘-’ ,’/’ , ‘*’ , ‘(’ and ‘)’ .

### Approach

For converting Prefix to Postfix we use a stack . The stack helps us store the operands. Whenever an operator is found , we pop two operands from the stack and push a new operand . The final element at the top of the stack will be our postfix expression .

### Algorithm

1. Scan all symbols one by one from right to left in the given prefix expression .

2. If the reading symbol is an operand , push it into the stack .

3. If the reading symbol is an operator , then a. Pop two expression from the stack , operand1 and operand2 , which is operand for the current operator b. Push operand1 + operand2 + operator into the stack

4. If there is no symbol left then stop the process . Top of the stack will have the required infix expression .

NOTE : ‘+’ denotes the concatenation of strings .

### Prefix to Postfix conversion example with dry run ### Implementation

```#include <bits/stdc++.h>
using namespace std;

bool isOperand(char ch){
return (ch>='a' && ch<='z') || (ch>='A' && ch <='Z');
}

string prefixToPostfix(string prefix) {
stack<string> st;

int len = prefix.size();
for (int i = len - 1; i >= 0; i--) {
if(isOperand(prefix[i])){

st.push(string(1,prefix[i]));

}
else{
string operand1=st.top();
st.pop();

string operand2=st.top();
st.pop();

st.push( operand1 + operand2  + string(1,prefix[i]));
}
}
return st.top();
}

int main() {