C++ Array of Bank accounts & Ask user to sort by name, id or balance.

Question

C++ question: I have a BankAccount class that has private member variables, string name, string id, and int balance. I made an array of 5 Bank Account objects that stored different names, bank balances, and id numbers, and I am required to allow a user to select whether they want to sort a bank account by name, id, or balance. I NEED to make a function using bubble sort code to sort through the array but I am not allowed to create a sort function for each member variable, what I mean by that is...if the user selects to sort by name or sort by balance, I can't call a sortbyname function or a sortbybalance function, I would call the same sort function for all, but I don't know how to do this.

Answer 1

// Here is one way of doing it

/* Add this enum type, listing possible criteria by which to sort

*/

typedef enum Criterion {

NAME,

ID,

BALANCE

} Criterion;

/* Add this class encapsulating comparison between two BankAccounts

*/

class BankAccountComparator {

Criterion criterion; // how to compare

public:

// Specify how this comparator should look at two BankAccounts

BankAccountComparator(Criterion c)

{

criterion = c;

}

/* This is the meat!

Return

a negative number if a < b

a positive number if a > b

0 if a == b

The meaning of <, >, == is given by the criterion

*/

int compare(BankAccount a, BankAccount b)

{

switch (criterion) {

case NAME: return a.name. compare(b.name); // use built-in string comparison

case ID: return a.id. compare(b.id); // use built-in string comparison

case BALANCE: return (a.balance < b.balance ? -1 :

a.balance > b.balance ? +1 : 0);

}

printf("%s: %d: Invalid criterion %d\n", __FILE__, __LINE__, criterion);

abort();

}

};

/* Modify your sort function to take an additional parameter:

a BankAccountComparator telling you how to compare BankAccounts

*/

void sort(BankAccount a[],

BankAccountComparator c)

{

/* Your usual code for the sort routine.

Except when you want to compare two elements you do it like this

*/

if (c.compare(a[i], a[j]) < 0) {

// whatever you do when a[i] < a[j]

}

}

{

// Somewhere in your main program where you invoke your sort() function

/* Before sorting, prepare a comparator according to user input.

*/

BankAccountComparator c(/* convert user input to a Criterion value*/);

/* Envoke your sort routine together with the comparator c

*/

sort(a, c);

}