I believe you're asking about creating a string, but I'm not certain. If not, this answer probably won't be useful:
sprintf() is just like printf() except that instead of writing to the standard output, it creates a string and writes that to the first argument. There's danger involved with sprintf(): it doesn't know how large your array is so it's possible to have an overflow, which is bad. In your code you know that x and y will never be larger than a particular value, so sprintf() can be used safely. That is, if your grid is 10x10, you know that the longest string you can make is 9 characters: room1010 plus one more character for the string terminator.
int x = 1, y = 3;
sprintf(location, "room%d%d", x, y);
If you use sprintf() just remember that it is dangerous. There is a replacement called snprintf() that is safe, but it's not as widely available as sprintf().