Is this a good function?

[gator6688]

void enterData(int date, char firstName, char lastName, double amount);

int _tmain(int argc, _TCHAR* argv[])
{

int date;
char firstName, lastName;
double amount;

enterData();
cin >> date;
enterData();
cin >> firstName;
enterData();
cin >> lastName;
enterData();
cin >> amount;

[gator6688]

Or do I need to put void enterData(int, char, char, double);?

[ilikepython]

Or do I need to put void enterData(int, char, char, double);?

For the prototype it doesn't matter. You should include the names for the definition though. However, in your exmaple, you are not passing any arguments to enterData().

[weaknessforcats]

I think you need to rethink this.

For example:

enterData();
cin >> date;

calls enterData() and then does an extract from the keyboard for the date, which is an int.

Question1 : What's the function for??
Question2 : Why does your function call have no arguments??
Question3 : How are you getting data back out of the function??
Question4 : Why do a cin >> if the data is entered in the function??

It looks like you are just starting to learn C++ so please post again when you get further along.