Won't add what it got from the other function each for loop cycle

#include <stdio.h>

//function to convert letter grade into a number
float GradePoints(char grade)
{
	float gP;

	switch (grade)
	{
	case 'A':
	case 'a':
		gP = 4.0;
		break;

	case 'B':
	case 'b':
		gP = 3.0;
		break;

	case 'C':
	case 'c':
		gP = 2.0;
		break;

	case 'D':
	case 'd':
		gP = 1.0;
		break;

	case 'F':
	case 'f':
		gP = 0.0;
		break;
	}

	return gP;
}


//function to calculate grade point average
float Gpa(char grades[], char hours[], int arrLength)
{
	//gradepoint * time in class
	float totalGpHours = 0;
	//time in class
	float totalHours = 0;
	//final grade point average 
	float gradePointAverage;
	int i;

	for (i = 0; i < arrLength; ++i)
	{
		//add the user input time in each class to get total time in class. this is the denominator
		totalHours = hours[i] + totalHours;
		//multiplies hours in class and number grade from that class and adds the product to totalGpHours. this is the numerator
		totalGpHours = totalGpHours + (GradePoints(grades[i]) * hours[i]);

	}

	//calculate grade point average
	gradePointAverage = totalGpHours / totalHours;

	return gradePointAverage;

}



int main()
{
	//add one more element to the array because of the null
	char grades[6];
	int classTime[5];
	int i;

	//Ask user for letter grades
	printf("Please enter the letter grades you received (upper-case letters, no spaces):\n");
	//gets input plus one for the array grades
	fgets(grades, 6, stdin);

	//Ask user for time in each class
	printf("Please enter the time you spent in each course(in hours)");

	for (i = 0; i < 5; ++i)
	{
		//add one to i so it looks normal for the user and you don't start at course 0
		printf("\n Course %d: ", i + 1);
		scanf("%d", &classTime[i]);
	}


	printf("\n");
	printf("Your grade point average is: %f\n\n", Gpa(grades, classTime, 5));


	getchar();

	return 0;
}