Need to see the calling sequence and error in context to tell, but...
- As you show it, you've thrown away the result of the routine so there wasn't any point in calling it to begin with-- use a return variable, and
- Do NOT use a global array for the data array; instead compute it wherever it is it needs be but again use an array in which to return its new value (can be the same as that with which you call it) and pass that to any other function(s) that need it.
- As you've written it, j is undefined in the first loop; variables are local within the scope of functions excepting for (ugly!) global ones which are as noted to be avoided if at all possible. Hence, defining the loop variable outside the function has no bearing; those h, j are entirely different variables than those using the same names inside the function. Besides, when you create the for loop, even if they were in the function they're being re-defined.
It's not clear what you want the function to return, an array or a single value for a given location as true/false. If the latter, may as well just test the location in the calling function; that's all it is. If a logical array for the input array, then no loops are needed, simply
isTaken=(tttArray==1); % logical array, T if position set
