clrscr() used to clear a text mode screen and clearscreen() cleared a graphical one. I still remember this because I spent 3 days trying to troubleshoot one of my university projects.
The assignment was to implement a system to take realtime data (simulated using a text file) and display it graphically with user configurable alert levels.
This was the basic Programming level 2 course (level 1 was Modula-2 (I still have nightmares)) and certainly not a problem for someone who already knew C years before right? HAH!
I was getting weird things going on, colours were not changing as they were meant to when the alert levels were crossed and I couldn't see any reason why. I tried every way possible in Borland C++ 3.1 to change those colours but they still did weird things. I couldn't find a bug in my code for love nor money, nor could my tutor. I even implemented my own ET4000 (my GFX card) colour mapping routine using TASM to programme the GFX card directly but got exactly the same results.
What was it? I had used clearscreen() to clear a text screen a bit earlier in my code. That's all it was and it took 3 days to find.
Now I remember why I like PHP so much