Typically it could be done something like this
I'm not sure that it is a good idea to give an example that makes any assumptions about what
I am finding it hard to even just add a char to char *.
means.
I find that people that make statements like this assume that pointers and arrays are the same thing. While there are strong ties between pointers and arrays, that is ONLY true when the pointer points to allocated memory. Far too often, newbies create a pointer that points to nothing, and then assume that they can use it as an array that holds as much as they want.
Rather than suggesting how they might do what they suggest in the question, I think it's better to ask them to post some code, so that it can be determined that the pointer in question does indeed point to allocated memory.