Input validation predicament

[Akintoc]

I'm currently working on a very simple program that takes in a students name, however many grades that student has, then averages the grades and outputs them. A condition that I want to meet, is that if the user inputs a "character" instead of a "int" for a grade, I want to be able to tell them it's wrong and ask them to re-enter the value.
Here's my code so far, its just missing the input verification bit:

char studentName[15];
int gradeCount;
float finalGrade, gradeSum, gradeCheck;
bool gradeLoop = true;

int _tmain(int argc, _TCHAR* argv[])
{
	cout<<"Please enter student's name."<<endl;//student name-------
	cin>>studentName;
	cout<<studentName<<"'s grades."<<endl;//student name---------

	cout<<"Enter student grade."<<endl;
	cin>>gradeCheck;
	
	
	while(gradeLoop)//grade loop---------
	{	
		if(gradeCheck >= 0 && gradeCheck <= 150)//user grade input check for the correct value limit
		{
			gradeSum += gradeCheck;//increments gradeSum
			cout<<"Current Grade Sum: "<<gradeSum<<endl;
			gradeCount++;//tracks the number of grades entered by the user
			cout<<"Number of Grades Entered: "<<gradeCount<<endl;
			cout<<"Enter student's next grade."<<endl;
		}
		else//check for negetive grade value, average calculated, and average output-------
		{
			finalGrade = (gradeSum/gradeCount);
			cout<<studentName<<"'s final grade:"<<setprecision(4)<<finalGrade<<endl;
			gradeLoop = false;
		}
		 cin>>gradeCheck;
		
	}//end grade while loop --------------------

	system ("pause");
	return 0;
}

what's the simplest way to verify if the user accidentally inputs a "char" instead of a numerical value?