problem with toupper()

[FenixRising]

Hi,

I am having trouble with this line of code:

cout << "Lower to upper: t" << toupper(str);

The str is underlined and it won't compile.

#include<iostream>
#include<string>
#include<cctype>

using namespace std;

void upr(const string & str);

int main()
{
	string strinpt;
	char quit = 'Q';
	while (quit != 'q')
	{
		cout << "Enter phrase in lower case to be turned into upper case: " << "\n";
		getline(cin, strinpt);
		upr(strinpt);
		cout << "Do you want stop entry? " << "\n";
		cin >> quit;
	}
	return 0;
}
void upr(const string & str)
{
	 cout << "OutPut: " << str << "\n";
	 cout << "Lower to upper: t" << toupper(str);
}

Any help would be appreciated.