How can I define a variable which has integer values?

I just started using mat-lab, and I searched the help, and I only found assumptions command, which doesn't work! it gives me the error : Undefined function 'assumptions' for input arguments of type

Actually, I want to draw a grid: I want to write a code which each time draw a grid of specified size (all the points should have integer coordinates)!

[dpb]

Not sure at all about what you mean by "draw a grid of specified size".

If you mean an axis w/ integer tick labels, simply use the range of 0:N and L:M, say as the values for x and y ticks.