strange problem with create new variable ...

[pointerToNull]

I created a new variable(for example : int i = 0 ) in my program and don't use that variable after that my program exit because one of my array data change and when I delete that variable , my array didn't change and program run without any problem .
I use memset function for initials my array data and I read a log from memory to program .
my program run in qt latest version.