If you want a string that is not constant, that would be assigned differently, and the answer would depend on whether you mean "assign memory space" or "assign the characters forming the string" when you say "assign", as these are two separate activities in C.
What do you want to know? What have you tried? What books and/or articles have you read, and what is it you do not understand? Who was that masked stranger?
It's really bad form to use this sort of naming in projects. None of those names have any significance in terms of what they are supposed to represent and, as you have discovered to your cost, it's easy to end up with basic errors such as the above.
[Agree 100% with this.]
To elaborate, the resource.h constants (ie. IDC_xxx) should have meaningful names, be numerically unique, the control/value variable names should be meaningful as well, and clearly related to the resource.h constants.