Example: Modular Bill Generator in C++

// Modular Bill Generator
#include <iostream>
#include <vector>
#include <string>
#include <iomanip>

// Define a structure for an item
struct BillItem {
    std::string name;
    int quantity;
    double price;
    double itemTotal; // Total for this specific item
};

// Function to get item details from user
void getItemDetails(BillItem& item, int itemCounter) {
    std::cout << "\nEnter details for Item " << itemCounter << ":\n";
    std::cout << "Enter item name: ";
    std::cin.ignore(); // Consume the newline character left by previous cin
    std::getline(std::cin, item.name);

    std::cout << "Enter quantity: ";
    std::cin >> item.quantity;

    std::cout << "Enter price per item: $";
    std::cin >> item.price;

    item.itemTotal = item.quantity * item.price;
}

// Function to calculate all totals
void calculateTotals(const std::vector<BillItem>& items, double& subtotal, double& taxAmount, double& grandTotal, double taxRate = 0.08) {
    subtotal = 0.0;
    for (const auto& item : items) {
        subtotal += item.itemTotal;
    }
    taxAmount = subtotal * taxRate;
    grandTotal = subtotal + taxAmount;
}

// Function to print the entire bill
void printBill(const std::vector<BillItem>& items, double subtotal, double taxAmount, double grandTotal, double taxRate = 0.08) {
    std::cout << "\n----------------------------------------\n";
    std::cout << std::setw(20) << "YOUR RECEIPT\n";
    std::cout << "----------------------------------------\n";
    std::cout << std::left << std::setw(15) << "Item"
              << std::right << std::setw(5) << "Qty"
              << std::right << std::setw(10) << "Price"
              << std::right << std::setw(10) << "Total\n";
    std::cout << "----------------------------------------\n";

    for (const auto& item : items) {
        std::cout << std::left << std::setw(15) << item.name
                  << std::right << std::setw(5) << item.quantity
                  << std::right << std::setw(10) << std::fixed << std::setprecision(2) << item.price
                  << std::right << std::setw(10) << std::fixed << std::setprecision(2) << item.itemTotal << "\n";
    }
    std::cout << "----------------------------------------\n";

    std::cout << std::left << std::setw(25) << "Subtotal:"
              << std::right << std::setw(15) << std::fixed << std::setprecision(2) << subtotal << "\n";

    std::cout << std::left << std::setw(25) << "Tax (" << (taxRate * 100) << "%):"
              << std::right << std::setw(15) << std::fixed << std::setprecision(2) << taxAmount << "\n";

    std::cout << "----------------------------------------\n";

    std::cout << std::left << std::setw(25) << "Grand Total:"
              << std::right << std::setw(15) << std::fixed << std::setprecision(2) << grandTotal << "\n";
    std::cout << "----------------------------------------\n";
    std::cout << "Thank You!\n";
}

int main() {
    std::vector<BillItem> items;
    double subtotal = 0.0;
    double taxAmount = 0.0;
    double grandTotal = 0.0;
    double taxRate = 0.08;
    char addMore = 'y';
    int itemCounter = 1;

    // Loop to get item details
    while (addMore == 'y' || addMore == 'Y') {
        BillItem currentItem;
        getItemDetails(currentItem, itemCounter); // Call function to get details
        items.push_back(currentItem);

        std::cout << "Add another item? (y/n): ";
        std::cin >> addMore;
        itemCounter++;
    }

    // Calculate all totals using a function
    calculateTotals(items, subtotal, taxAmount, grandTotal, taxRate);

    // Print the bill using a function
    printBill(items, subtotal, taxAmount, grandTotal, taxRate);

    return 0;
}