Look at the commented lines of where I edited your code. I did the first statement for you, look at http://www.asciitable.com for info on the rest...

Code:
#include <iostream>

using namespace std;

int main()

{
	int A;	//int not float					


	cout << "Enter any character then press enter:" << endl; 
	cin >> A;											
	
	if 	(A>=65 && A<=90)  //because ascii characters 65 through 90 are Upper Case letters.
												
		cout << "The character you entered was a Upper-Case Letter" << endl;		
		
	else if	(statement2)
												
		cout << "The character you entered was a Lower-Case Letter" << endl;		
		
	else if (statement3)
		cout << "The character you entered was a Digit" << endl;
		
		else											
		cout << "The character you entered was none of the above" << endl;	


return 0;
}