Function to Withdraw amount from an array of balance - c++

Question

I'm to write a function to withdraw money from array containing initial balance.
If the balance is insufficient, then a warning message along with user's balance is displayed.
The user is prompted to enter the new amount for a second time, if the amount is OK withdraw operation is completed and balance is updated and menu is displayed.
If balance is still insufficient, withdraw operation is terminated and menu is displayed.
Below is the code which works if I try to enter amount which is lower than the balance for the first time. But does not update the balance well if I enter the valid amount on the second try.
double withdrawAmount(int pin, double balance[]){
double amount;
double newBalance = balance[pin];
int withdrawTrial = 0;
do{
system("cls");
cout << "-----------------------------------------" << endl;
cout << "\tWELCOME TO EDON ATM" << endl;
cout << "-----------------------------------------" << endl;
cout << endl;
cout << "Please enter amount to be withdrawn: $";
cin >> amount;
if (balance[pin] < amount){
cout << endl;
cout << "Insufficient Balance!" << endl;
cout << "Your balance is: $" << balance[pin] << endl;
cout << endl;
while (withdrawTrial < 1){
withdrawTrial++;
cout << "Please enter amount to be withdrawn: $";
cin >> amount;
}
if (withdrawTrial == 1){
menuBoard();
return newBalance;
}
}
balance[pin] -= amount;
newBalance = balance[pin];
} while (amount < 0);
return newBalance;
}

Answer 1

You are not following the instructions correctly. You are not validating the user's input on the second prompt. Get rid of the while (withdrawTrial < 1) loop completely. Prompt once and validate. If the amount is greater than the available balance then prompt again and re-validate. If the amount is still greater than the available balance then exit. No loops are needed (unless you want to validate the user is actually entering a floating-point number and nothing else).
Also, you should not be calling menuBoard() inside of withdrawAmount() itself, you should be calling it after withdrawAmount() exits.
double inputDollars(const char *prompt){
double value;
do {
cout << prompt << ": $";
if (cin >> value)
break;
cout << endl;
cout << "Invalid Input!" << endl;
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
}
while (true);
return value;
}
double withdrawAmount(int pin, double balance[]){
double amount;
system("cls");
cout << "-----------------------------------------" << endl;
cout << "\tWELCOME TO EDON ATM" << endl;
cout << "-----------------------------------------" << endl;
cout << endl;
amount = inputDollars("Please enter amount to be withdrawn");
if (balance[pin] < amount){
cout << endl;
cout << "Insufficient Balance!" << endl;
cout << "Your balance is: $" << balance[pin] << endl;
cout << endl;
amount = inputDollars("Please enter amount to be withdrawn");
if (balance[pin] < amount){
cout << endl;
cout << "Insufficient Balance!" << endl;
return balance[pin];
}
}
balance[pin] -= amount;
return balance[pin];
}
...
double balances[N];
int pin;
...
withdrawAmount(pin, balances);
menuBoard();