toUpper error

[Sunny101]

Here's the segment of my code:

void main()
{
	char choice;

	do
	{
		double WholeSale = GetWholeSale();
		double getMark = GetMark();
		double catchretail = CalculateRetail( WholeSale , getMark);
		Report (catchretail);

		
		cout << " Do you want to do another markup? Y for yes and N for no:  ";
		cin >> choice;
		choice = toUpper (choice);
	}
	while ( choice == 'y' );
}

I am getting these two errors:

Error 1 error C3861: 'toUpper': identifier not found 45
2 IntelliSense: identifier "toUpper" is undefined

help please? (:

[Stewbond]

Try:
choice = toupper (choice);

Function calls are case sensitive.