Inventory Program

#include <iostream>
#include <fstream>
#include <cctype>
#include <cstdio>
using namespace std;

struct Inventory {
  string description;
  int quantity;
  double wholesaleCost;
  double retailCost;
  string dateAdded;
};

void prompt();
void addItem(fstream &);
void viewItem(fstream &);
void modifyItem(fstream &);
void validate(int *);
void validate(double *);
string getDate();
string validateDate(string);

int main() {
  char userChoice;
  fstream invFile("inventory.txt", ios::in | ios::out | ios::app);

  if (invFile.fail()) // creates file if a file does not already exist
  {
    invFile.open("inventory.txt");
    invFile.close();
  }

  do {
    prompt();
    cin >> userChoice;

    while(!isdigit(userChoice)) {
      cout << "Enter a digit only.\nEnter choice: ";
      cin >> userChoice;
    }

    switch(userChoice) {
      case '1':
        addItem(invFile);
        break;
      case '2':
        viewItem(invFile);
        break;
      case '3':
        modifyItem(invFile);
        break;
    }
  } while(userChoice != '4');

  invFile.close();

  return 0;
}

void prompt() {
  cout << "Choose from the following.\n";
  cout << "1. Add new record(s) to the file.\n";
  cout << "2. Display any record(s) in the file.\n";
  cout << "3. Change any record(s) in the file.\n";
  cout << "4. Exit\n";
  cout << "Enter choice: ";
}

void addItem(fstream& file) {
  Inventory item;
  string date;

  cout << "Enter the description of the item: ";
  cin >> item.description;
  file << "Description: " << item.description << endl;
  string itemDesc = item.description;

  cout << "Enter the quantity of " << itemDesc << ": ";
  cin >> item.quantity;
  validate(&item.quantity);
  file << "Quantity: " << item.quantity << endl;

  cout << "Enter the Wholesale Cost of " << itemDesc << ": $";
  cin >> item.wholesaleCost;
  validate(&item.wholesaleCost);
  file << "Wholesale Cost $" << item.wholesaleCost << endl;

  cout << "Enter the Retail Cost of " << itemDesc << ": $";
  cin >> item.retailCost;
  validate(&item.retailCost);
  file << "Retail Cost $" << item.retailCost << endl;

  item.dateAdded = getDate();
  file << "Date added: " << item.dateAdded << "\n\n";
}

void viewItem(fstream& file) {
  file.close();
  file.open("inventory.txt");
  // closing and re-opening the file helps ensure that the file is being read from the beginning
  string desc, line;

  cout << "Enter the name of the item you want to display from the record(s): ";
  cin >> desc,
  desc = "Description: " + desc;
  getline(file, line); // gets the first line of the file

  while(true) {
    if(line == desc) { // if the matching item is found, it will display the 5 lines of corresponding info on that item
      for(int i = 0; i < 6; i++) {
        cout << line << endl;
        getline(file, line);
      }
    }

    getline(file, line); // gets the next line of the file

    if(file.eof()) { // conditional to break out of the loop once the end of the file is reached
      break;
    }
  }
}

void modifyItem(fstream& file) {
  fstream temp("temp.txt", ios::out);
  string desc, line;

  cout << "Enter the name of the item you want to modify from the record(s): ";
  cin >> desc,
  desc = "Description: " + desc;

  getline(file, line);

  while(line != desc) {
    temp << line << endl;
    getline(file, line);
  }

  if(line == desc) {
    addItem(temp);
  }

  while(true) {
    if(line == desc) {
      for(int i = 0; i < 6; i++) {
        getline(file, line);
      }
    }

    temp << line << endl;
    getline(file, line);

    if(file.eof()) {
      break;
    }
  }

  file.close();
  temp.close();

  remove("inventory.txt");
  rename("temp.txt", "inventory.txt");
  if( remove( "temp.txt" ) != 0 )
    perror( "Error deleting file" );
  else
    puts( "File successfully deleted" );
}

string getDate() {
  string date;

  cout << "Enter the date that the item was added to the inventory (mm/dd/yyyy): ";
  cin >> date;
  date = validateDate(date);

  return date;
}

string validateDate(string date) {
  for(int i = 0; i < 11; i++) {
    if(i == 0 || i == 1 || i == 3 || i == 4 || i == 6 || i == 7 || i == 8 || i == 9) {
      if(!(isdigit(date[i]))) {
        cout << "Invalid date format!\n";
        getDate();
      }
    }

    else if(i == 2 || i == 5) {
      if(date[i] != '/') {
        cout << "Invalid date format!\n";
        getDate();
      }
    }
  }

  return date;
}

void validate(int *num) {
  while(*num < 0) {
    cout << "No negative numbers allowed.\nPlease enter a non-negative value: ";
    cin >> *num;
  }
}

// validate function that takes a double as a parameter
void validate(double *num) {
  while(*num < 0) {
    cout << "No negative numbers allowed.\nPlease enter a non-negative value: ";
    cin >> *num;
  }
}