Stack_InfixToPostfix.cpp

#include <iostream>

using namespace std;


class inpo {
    char in[20], po[20], stk[10];
    int i, j, is, ic, top, top1;
    int stk1[10];
public:
    inpo() {
        i = j = is = ic = 0;
        top = top1 = -1;
    }

    bool IsOperand(char C) {
        if (C >= '0' && C <= '9') return true;
        if (C >= 'a' && C <= 'z') return true;
        if (C >= 'A' && C <= 'Z') return true;
        return false;
    }

    void getinfix() {
        cout << "\nEnter valid infix expression: ";
        cin >> in;
    }

    void showinfix() {
        cout << "\t" << in;
    }

    int isempty() {
        if (top == -1)
            return 1;
        else
            return 0;
    }

    int isfull() {
        if (top == 9)
            return 1;
        else
            return 0;
    }

    void push1(int x1) {
        top = top + 1;
        stk1[top] = x1;
    }

    int pop1() {
        int s1;
        s1 = stk1[top];
        top = top - 1;
        return s1;
    }

    void push(char x) {
        top = top + 1;
        stk[top] = x;
    }

    char pop() {
        char s;
        s = stk[top];
        top = top - 1;
        return s;
    }

    void showpostfix() {
        cout << "\t" << po;
    }

    void convert();

    int instackprio();

    int incomingprio(char);

    void postfixExpEval();
};

void inpo::postfixExpEval() {
    i = 0;
    char ch;
    int op1, op2, res, tot;
    while (po[i] != '\0') {
        ch = po[i];
        if ((ch == '+') || (ch == '-') || (ch == '*') || (ch == '/') ||
            (ch == '^')) {
            switch (ch) {
                case '+':
                    op2 = pop1();
                    op1 = pop1();
                    res = op1 + op2;
                    push1(res);
                    break;
                case '-':
                    op2 = pop1();
                    op1 = pop1();
                    res = op1 - op2;
                    push1(res);
                    break;
                case '*':
                    op2 = pop1();
                    op1 = pop1();
                    res = op1 * op2;
                    push1(res);
                    break;
                case '/':
                    op2 = pop1();
                    op1 = pop1();
                    res = op1 / op2;
                    push1(res);
                    break;
                case '^':
                    op2 = pop1();
                    op1 = pop1();
                    res = op1;
                    while (op2 > 1) {
                        res = res * op1;
                        op2--;
                    }
                    push1(res);
                    break;
            }
        } else if (IsOperand(ch)) {
            push1(ch - '0');
        }
        i = i + 1;
    }
    tot = pop1();
    cout << "\nResult is:" << tot;
}

void inpo::convert() {
    i = j = 0;
    char p, k;
    while (in[i] != '\0') {
        p = in[i];
        if ((p == '(') || (p == '+') || (p == '-') || (p == '*') || (p == '/') || (p == '^') || (p == ')')) {
            if (isempty()) {
                push(p);
            } else if (p ==
                       ')') {
                k = pop();
                while (k != '(') {
                    po[j] = k;
                    j++;
                    k = pop();
                }
            } else {
                is = instackprio();
                ic = incomingprio(p);
                if (is > ic) {
                    k = pop();
                    po[j] = k;
                    j++;
                    push(p);
                } else {
                    push(p);
                }
            }
        } else {
            po[j] = p;
            j++;
        }
        i = i + 1;
    }
    if (in[i] == '\0') {
        while (!isempty()) {
            k = pop();
            po[j] = k;
            j++;
        }
    }
    po[j] = '\0';
}

int inpo::instackprio() {
    char b;
    b = stk[top];
    switch (b) {
        case '(':
            return 0;
        case '+':
            return 2;
        case '-':
            return 2;
        case '*':
            return 4;
        case '/':
            return 4;
        case '^':
            return 5;
    }
    return 0;
}

int inpo::incomingprio(char ch) {
    switch (ch) {
        case '(':
            return 9;
        case '+':
            return 1;
        case '-':
            return 1;
        case '*':
            return 3;
        case '/':
            return 3;
        case '^':
            return 6;
    }
    return 0;
}

int main() {
    inpo p1;
    p1.getinfix();
    p1.showinfix();
    cout << "\nAfter conversion from infix to postfix: ";
    p1.convert();
    p1.showpostfix();
    cout << "\nPostfix expression is as follows: ";
    p1.postfixExpEval();
    return 0;
}