Iterative procedure naming

I have a process running multiple times over a picture. I would like to save each intermediate picture result using a increasing name;

Ie iteration1.png, iteration2.png, etc. The number of iterations may change between each execution.

I am having trouble creating the name.

I am using char strings and not strings for the name (thats just the way it is, I have received functions that use it like this).

How would I code name = "iteration"+iter+".png"?

I have tried strcat, I have tried with addition (+).

Thanks