循环变量的值突然变化

i am trying to run a loop from january1 2015 to current date and fill value of each day in database. I am using a julian day counter as loop variable. No where inside the loop i am changing the value of counter but after looping 2 times the value of counter changes abruptly to garbage values. What can be the reason?i am trying to run a loop from january1 2015 to