RzQ0Dc - Online C++ Compiler & Debugging Tool

#include <iostream>
#include <stack>
using namespace std;

// Original function with nested blocks
void F(int n) {
    int x = n * 2;
    int y = n + 3;
    int z = 0;

    // Block 1
    if (n > 0) {
        int a = x + 1;
        int b = y - 1;

        // Block 2
        {
            int d = a * 2;
            int e = b / 2;
            z += d + e;
        }
    }

    // Block 3
    if (n > 1) {
        int f = y + 10;
        int g = x - 5;
        z += f - g;
    }

    cout << "F(" << n << "): " << z << endl;
}

// Iterative implementation with single fb variable
struct ActivationRecord {
    int n;
    int x, y, z;  // Persistent variables

    // Temporary variables (only one set used at a time)
    int temp1, temp2;

    int fb; // Current flattened block (0-3)

    ActivationRecord(int n) : n(n), x(0), y(0), z(0), fb(0) {}
};

void G(int n) {
    stack<ActivationRecord> st;
    st.push(ActivationRecord(n));

    while (!st.empty()) {
        ActivationRecord& ar = st.top();

        switch (ar.fb) {
            case 0: // Initialization
                ar.x = ar.n * 2;
                ar.y = ar.n + 3;
                ar.z = 0;
                ar.fb = 1;
                break;

            case 1: // Block 1
                if (ar.n > 0) {
                    ar.temp1 = ar.x + 1; // a
                    ar.temp2 = ar.y - 1; // b
                    ar.fb = 2;
                } else {
                    ar.fb = 3;
                }
                break;

            case 2: // Block 2
            {
                int d = ar.temp1 * 2; // using temp1 as a
                int e = ar.temp2 / 2; // using temp2 as b
                ar.z += d + e;
                ar.fb = 3;
                break;
            }

            case 3: // Block 3
                if (ar.n > 1) {
                    ar.temp1 = ar.y + 10; // f
                    ar.temp2 = ar.x - 5;  // g
                    ar.z += ar.temp1 - ar.temp2;
                }
                cout << "G(" << ar.n << "): " << ar.z << endl;
                st.pop();
                break;
        }
    }
}

int main() {
    cout << "Original function F():\n";
    for (int i = 0; i < 5; i++) F(i);

    cout << "\nIterative version G():\n";
    for (int i = 0; i < 5; i++) G(i);

    return 0;
}