def main():
instanceHistogram = Histogram("ABCDF")
dataset = open('score_transcript.txt', "r")
for each_line in dataset:
letter_grade = scoreToLetterGrade(int(each_line))
instanceHistogram.increaseCount(letter_grade)
# when for loop exit, the five category have finished their statistic, ready for subsequently display
gen_chart(instanceHistogram)
