Converting the name of a file into a c-string - c++

Question

I am trying to open a .dat file to use as an input for my program. The assignment says I need to convert the name I enter for the file name into c-string datatype so it can be read through the .open("") command. My program compiles but I'm sure I'm doing something wrong when I try to convert file name. I have looked around for people with similar problems but I've had no luck so any suggestions you can give me would be much appreciated!
Here is the function where I attempt to open the file, and the other function where I try to convert the file name.
int main()
{
ifstream fp;
string name[SIZE], filename;
int counter, idx = 0;
float rate[SIZE], sum[SIZE], gross[SIZE], with[SIZE], pay[SIZE], net[SIZE], hours[SIZE];
getfile(fp, filename);
readFile(fp, name, rate, hours);
pay[SIZE] = calcPay(rate, sum);
gross[SIZE] = calcGross(pay);
with[SIZE] = calcAmount(gross);
net[SIZE] = calcNet(gross, with);
output(name, rate, sum, with, gross, net, pay, SIZE);
return 0;
}
//Convert filename into C-string
string convert(ifstream &fp, string filename)
{
fp.open(filename.c_str());
return filename;
}
//Get file name from user.
void getfile(ifstream &fp, string filename)
{
cout <<" Enter the name of the file: ";
cin>>filename;
convert(fp, filename);
fp.open("filename");
if (!fp)
{
cout<<"Error opening file\n";
exit (1);
}
}

Answer 1

cout <<" Enter the name of the file: ";
cin>>filename;
convert(fp, filename);
fp.open("filename");
was probably meant to be (in case of present C++11 support):
cout << " Enter the name of the file: ";
cin >> filename;
fp.open(filename);
or (in C++03):
cout << " Enter the name of the file: ";
cin >> filename;
fp.open(filename.c_str());
Side note: Elements in an array are indexed from 0 to SIZE - 1 so when you declare:
float pay[SIZE];
then when you do:
pay[SIZE] = calcPay(rate, sum);
you are accessing memory "pass" the last element, which causes undefined behavior.