if (score < 70 && score >= 0) 
		if (score >= 70 && score <= 76)
			if (score >= 77 && score <= 86)
				if (score >= 87 && score >= 78)
					if (score >= 94 && score <= 100)
						if (score < 0 || score > 100)
							cout << "Grade must be between 0 and 100!\n";
						else
							cout << "Invalid input!\n";
					else
					  grade = 'A';
				else
					grade = 'B';
			else
				grade = 'C';
		else
			grade = 'D';
	else
		grade = 'F';