GPA Error Test | Python Fiddle

# PSU 161
# Debugging Example
# Can you find the error?
# Hint: Try a grade point that includes a C-

grade = ""
creditHours = 0
index = 0
pointValue = 0
qualityPoints = 0
accumulatedQPoints = 0
accumulatedCHours = 0

# This is the
grades = ("A", "A-", "B+", "B", "B-","C+", "C", "C-","D+", "D", "D-","F")
gradeValues = (4.0, 3.67, 3.33, 3.0, 2.67, 2.33, 2.0, 10.67, 1.33, 1.0, .67, 0.0)

print ("Welcome to the GPA calculator.")
grade = input ("Enter a grade (or STOP to stop and compute GPA) ")
creditHours = int(input("How many credits was this class? "))

# What happens if I type STOP right off the bat? Is that also a semantic error?                 
while (grade != "STOP"):
    index = grades.index(grade)
    pointValue = gradeValues[index]
    qualityPoints = pointValue * creditHours
    accumulatedQPoints = accumulatedQPoints + qualityPoints
    accumulatedCHours = accumulatedCHours + creditHours
        
    grade = input ("Enter a grade (or STOP to stop and compute GPA) ")
    if (grade == "STOP"):
        break
    credit = int(input("How many credits was this class? "))

print ("The GPA is:", round(accumulatedQPoints / accumulatedCHours, 2))

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