Question

this is my code I want the opposite i want to convert a postfix expression to infix expression

#include <iostream>

#include <string>

#define SIZE 50

using namespace std;

// structure to represent a stack

struct Stack {

  char s[SIZE];

  int top;

};

void push(Stack *st, char c) {

  st->top++;

  st->s[st->top] = c;

}

char pop(Stack *st) {

  char c = st->s[st->top];

  st->top--;

  //(A+B)*(C+D)

  return c;

}

/* function to check whether a character is an operator or not.

this function returns 1 if character is operator else returns 0 */

int isOperator(char c) {

  switch (c)

  {

  case '^':

  case '+':

  case '-':

  case '*':

  case '/':

  case '%':

  return 1;

  default:

  return 0;

  }

}

/* function to assign precedence to operator.

In this function we assume that higher integer value means higher precedence */

int precd(char c) {

  switch (c)

  {

  case '^':

  return 3;

  case '*':

  case '/':

  case '%':

  return 2;

  case '+':

  case '-':

  return 1;

  default:

  return 0;

  }

}

//function to convert infix expression to postfix expression

string infixToPostfix(Stack *st, string infix) {

  string postfix = "";

  for(int i=0; i<infix.length(); i++)

     {

     if(isOperator(infix[i])==1)

     {

  while(st->top!=-1 && precd(st->s[st->top]) >= precd(infix[i]))

  postfix += pop(st);

  push(st,infix[i]);

     }

     else if(infix[i] == '(')

  push(st,infix[i]);

  

     else if(infix[i] == ')')

     {

  while(st->top!=-1 && st->s[st->top] != '(')

  postfix += pop(st);

  pop(st);

     }

     else

  postfix += infix[i];

  

  }

  while(st->top != -1)

  postfix += pop(st);

return postfix;

}

int main() {

  Stack st;

  st.top = -1;

  string infix;

  cout << "Enter an infix expression: ";

  getline(cin, infix);

  cout << "Postfix expression is: " << infixToPostfix(&st, infix);

  

  return 0;

}

Answer 1

#include <bits/stdc++.h>
using namespace std;
bool isOperand(char x) {
   return (x >= 'a' && x <= 'z') || (x >= 'A' && x <= 'Z');
}
string PostfixToInfix(string postfix) {
   stack<string> infix;
   for (int i=0; postfix[i]!='\0'; i++) {
      if (isOperand(postfix[i])) {
         string op(1, postfix[i]);
         infix.push(op);
      } else {
         string op1 = infix.top();
         infix.pop();
         string op2 = infix.top();
         infix.pop();
         infix.push("{"+op2+postfix[i]+op1 +"}");
      }
   }
   return infix.top();
}
int main() {
   string infix, postfix;
   cout<<"Enter a POSTFIX expression:<< postfix << endl;
   cin>> postfix;
   cout<<"POSTFIX Expression: "<< postfix << endl;
   infix = PostfixToInfix(postfix);
   cout<< endl << "INFIX Expression: " << infix;
   return 0;
}