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I'm looking for a better way to define a global variable. This is just a small banking app to practice using functions. Is this the correct way to define the variable according to C++ standards? I'm not 100% sure on this one. I defined it outside of main(), but if I remember correctly, this is a no no. I tried creating classes, I tried creating paramaters for the functions, this is the only way I could figure out how to get the variable to all the functions.

// banking.cpp : This file contains the 'main' function. Program execution begins and ends there. #include <iostream> using namespace std; int total = 100; void menu(); int deposit(); int withdraw(); int main() { menu(); return 0; } void menu() { int selection; cout << "your total money right now is $" << total << endl; cout << "select 1 for deposit." << endl; cout << "select 2 for withdraw" << endl; cin >> selection; switch (selection) { case 1: deposit(); break; case 2: withdraw(); break; } } int deposit() { int depositAmount; cout << "your current total is $" << total << endl; cout << "how much would you like to deposit? " << endl; cin >> depositAmount; total = depositAmount + total; cout << "your new total is $" << total << endl; cout << "you will be returned to the main menu..." << endl; menu(); return total; } int withdraw() { int withdrawAmount; cout << "your current total is $" << total << endl; cout << "how much would you like to withdraw? " << endl; cin >> withdrawAmount; total = total - withdrawAmount; cout << "your new total is $" << total << endl; cout << "you will be returned to the main menu..." << endl; menu(); return total; }
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    The usage of non-const globals is discouraged but your syntax for declaring it is correct. Commented Oct 28, 2020 at 15:19
  • See How to declare a global variable in C++ but in this specific case you could use a local variable and pass it around as function parameters. Commented Oct 28, 2020 at 15:20
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    I'm looking for a better way to define a global variable -- "Global variable" and "better" are two phrases that do not go together. Commented Oct 28, 2020 at 15:20
  • I think you've declared global variable. And in the same way the only correct way to declare global variable - not to declare and not to use it whenever you can. Commented Oct 28, 2020 at 15:20
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    This looks like it would be better to have a class with total as a member variable and deposit and withdraw as member functions. Commented Oct 28, 2020 at 15:22

2 Answers 2

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If you need to store a state shared across functions, you probably want to create a class/struct, with members as the data you want to share.

class MyClass { public: void menu(); int deposit(); int withdraw(); private: int total = 100; };

Then use this class whenever you want to run your logic.

int main() { MyClass myclass; myclass.menu(); return 0; }
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One further step in refinement: turn menu() back into a free function. It's part of a banking application, but not part of a bank account. +1.
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You can pass total to a function with & in front of it. It is known as reference in C++ and you can modify given object inside a function, not only it's copy. Examples. And in your code:

int deposit(int &total) { ...your code... }

Overall I don't think calling menu inside every function is a good idea. With each function call you push it to a stack, which takes extra memory. Changing deposit and withdraw to void and using while(1) loop inside of main() to call menu() would be much better.

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Thank you sooooooooo much, i knew there was something going to bite me in the end by stacking the menu options. you answered my question perfectly! I do appreciate that, thank you.

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