This is a sign of some bad code design:
str_saveas="HW_2_%d_micron_particle
z=d*10^6;
str_saveas=sprintf(str_saveas,z)
because you are putting meta-data into variable names. This is a very bad practice, and will only make your code slow, buggy, and complicated. This is exactly the problem you are experiencing now, although you probably don't realize it yet.
Read this to know why putting meta-data into variable names is a bad idea:
Some beginners think that putting meta-data into variable names is cunning and neat. It isn't, and it just causes them to write complex, buggy, slow code.
You should learn to use indexing: simple, efficient, neat, easy to write and debug. If you had used indexing then your example could be reduced down to two or three simpler lines of code.
