D-27_completed.cpp

#include <iostream>
using namespace std;

class stack
{
public:
    char stack_array[50];
    int top;
    stack()
    {
        top = -1;
    }
    void push(char symbol)
    {
        if (full())
            cout << "\nStack overflow:\n";
        else
        {
            top = top + 1;
            stack_array[top] = symbol;
        }
    }
    char pop()
    {
        if (empty())
            return ('#'); // Return value '#' indicates stack is empty
        else
            return (stack_array[top--]);
    }
    int empty()
    {
        if (top == -1)
            return (1);
        else
            return (0);
    }
    int full()
    {
        if (top == 49)
            return (1);
        else
            return (0);
    }

private:
    char infix[50];
    char postfix[50];

public:
    void read()
    {
        cout << "\nEnter an infix expression:";
        cin >> infix;
    }
    int white_space(char symbol)
    {
        if (symbol == ' ' || symbol == '\t' || symbol == '\0')
            return 1;
        else
            return 0;
    }
    void ConvertToPostfix()
    {
        int prev, p;
        char entry;
        p = 0;
        for (int i = 0; infix[i] != '\0'; i++)
        {
            if (!white_space(infix[i]))
            {
                switch (infix[i])
                {
                case '(':
                    push(infix[i]);
                    break;
                case ')':
                    while ((entry = pop()) != '(')
                        postfix[p++] = entry;
                    break;
                case '+':
                case '-':
                case '*':
                case '/':
                    if (!empty())
                    {
                        prev = prior(infix[i]);
                        entry = pop();
                        while (prev <= prior(entry))
                        {
                            postfix[p++] = entry;
                            if (!empty())
                                entry = pop();
                            else
                                break;
                        }
                        if (prev > prior(entry))
                            push(entry);
                    }
                    push(infix[i]);
                    break;
                default:
                    postfix[p++] = infix[i];
                    break;
                }
            }
        }
        while (!empty()) 
            postfix[p++] = pop();
        postfix[p] = '\0';
        cout << "\nThe postfix expression is: " << postfix << endl;
    }
    int prior(char symbol)
    {
        switch (symbol)
        {
        case '/':
            return (4); 
        case '*':
            return (3); 
        case '+':
            return (2); 
        case '-':
            return (1); 
        case '(':
            return (0); 
        default:
            return (-1);
        }
    }
};

int main()
{
    char choice = 'y';
    stack expr;
    while (choice == 'y')
    {
        expr.read();
        expr.ConvertToPostfix();
        cout << "\n\nDo you want to continue ? (y/n): ";
        cin >> choice;
    }
    return 0;
}