Question

write a program to evaluate the following postfix expression. the value of each variable must be asked from the user during the execution time. suppose the postfix expression is tom jerry mickey 23 * - $ and variables tom, jerry, and mickey are int type

Answer 1

In this exercise we have to use the knowledge of computational language in C++ to write a code that program to evaluate the following postfix expression. the value of each variable must be asked from the user during the execution time.

Writting the code:

#include <bits/stdc++.h>

using namespace std;

// CREATED A CLASS STACK

class Stack

{

public:

int top;

unsigned sz;

int* ar;

};

// VARIOUS STACK FUNCTIONS

Stack* makeStack( unsigned sz )

{

Stack* stack = new Stack();

// BASE CONDITION

if (!stack) return NULL;

stack->top = -1;

stack->sz = sz;

stack->ar = new int[(stack->sz * sizeof(int))];

if (!stack->ar) return NULL;

// RETURNING THE STACK

return stack;

}

// CHECKING IF THE STACK IS EMPTY

int isEmpty(Stack* stack)

{

return stack->top == -1 ;

}

// CHECKING THE TOP OF THE STACK

int whatAtTop(Stack* stack)

{

return stack->ar[stack->top];

}

// POPPING OUT OF A STACK

int pop(Stack* stack)

{

if (!isEmpty(stack))

 return stack->ar[stack->top--] ;

return '$';

}

// PUSHING IN THE STACK

void push(Stack* stack, int op)

{

stack->ar[++stack->top] = op;

}

// EVALUATING POSTFIX STARTS HERE

int postfixEvaluator(string res)

{

// CREATING STACK

Stack* stack = makeStack(res.length());

int i;

// BASE CONDITION

if (!stack) return -1;

for (i = 0; res[i]; ++i)

{

 // CHECK FOR SPACES

 if (res[i] == ' ')continue;

 // CHECK FOR THE DIGIT

 else if (isdigit(res[i]))

 {

  int N = 0;

  // EXTRACT THE NUMBER OUT OF STACK

  while (isdigit(res[i]))

  {

   N = N * 10 + (int)(res[i] - '0');

   i++;

  }

  i--;

  // PUSH THE NUMBER IN STACK

  push(stack, N);

 }

 // POPPING AND ARITHMETIC OPERATIONS

 else

 {

  int pos1 = pop(stack);

  int pos2 = pop(stack);

  switch (res[i])

  {

  case '+': push(stack, pos2 + pos1); break;

  case '-': push(stack, pos2 - pos1); break;

  case '*': push(stack, pos2 * pos1); break;

  case '/': push(stack, pos2 / pos1); break;

  }

 }

}

return pop(stack);

}

// MAIN CODE

int main()

{

string tes;

getline(cin, tes);

string tmp = "";

string res = "";

for (int i = 0; i < tes.length(); i++) {

 if (tes[i] <= 'z' and tes[i] >= 'a') {

  tmp += tes[i];

 } else if (tes[i] == ' ' and (tes[i - 1] <= 'z' and tes[i - 1] >= 'a')) {

  cout << "Enter the value of " << tmp << ": ";

  int x; cin >> x;

  res += (to_string(x));

  res += ' ';

  tmp = "";

 } else {

  res += tes[i];

 }

}

cout << "\nThe postfix expression is : " << res;

cout << "\nThe result is : " << postfixEvaluator(res);

return 0;

}

See more about C++ at brainly.com/question/19705654

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