To help with potential debugging problems, here is one example Part 1 run annotated with the account balance and interest balance at the end of each simulated day in a five week simulation.
~/$ ./part1
run 5 foo.txt
day 01: start-of-day balance = 700, end-of-day balance = 700
day 02: start-of-day balance = 700, end-of-day balance = 700
day 03: start-of-day balance = 700, end-of-day balance = 700
day 04: start-of-day balance = 700, end-of-day balance = 700
day 05: start-of-day balance = 700, end-of-day balance = 700
day 06: start-of-day balance = 700, end-of-day balance = 700
day 07: start-of-day balance = 700, end-of-day balance = 700
day 08: start-of-day balance = 700, end-of-day balance = 700
day 09: start-of-day balance = 700, end-of-day balance = 700
day 10: start-of-day balance = 700, end-of-day balance = 700
day 11: start-of-day balance = 700, end-of-day balance = 700
day 12: start-of-day balance = 700, end-of-day balance = 700
day 13: start-of-day balance = 700, end-of-day balance = 1250
day 14: start-of-day balance = 1250, end-of-day balance = 1250
day 15: start-of-day balance = 1250, end-of-day balance = 1250
day 16: start-of-day balance = 1250, end-of-day balance = 1250
day 17: start-of-day balance = 1250, end-of-day balance = 1250
day 18: start-of-day balance = 1250, end-of-day balance = 1250
day 19: start-of-day balance = 1250, end-of-day balance = 1250
day 20: start-of-day balance = 1250, end-of-day balance = 1250
day 21: start-of-day balance = 1250, end-of-day balance = 1250
day 22: start-of-day balance = 1250, end-of-day balance = 1250
day 23: start-of-day balance = 1250, end-of-day balance = 1250
day 24: start-of-day balance = 1250, end-of-day balance = 1250
day 25: start-of-day balance = 1250, end-of-day balance = 1250
day 26: start-of-day balance = 1250, end-of-day balance = 1250
day 27: start-of-day balance = 1250, end-of-day balance = 1800
day 28: start-of-day balance = 1800, end-of-day balance = 1800
day 29: start-of-day balance = 1800, end-of-day balance = 1800
day 30: start-of-day balance = 1800, end-of-day balance = 1800
day 31: start-of-day balance = 1800, end-of-day balance = 1800
day 32: start-of-day balance = 1800, end-of-day balance = 1800
day 33: start-of-day balance = 1800, end-of-day balance = 1800
day 34: start-of-day balance = 1800, end-of-day balance = 1800
day 35: start-of-day balance = 1800, end-of-day balance = 1800
Ending balance = 1800
Average end-of-day balance = 1202.86