Please explain me WHY!

[MarcBergeron]

Try adding this to your loading values:

trisC = %00000000


This will set your portC as outputs.
The zeros fromleft to right are portC.7, portC.6, portC.5, portC.4, portC.3, portC.2, portC.1, portC.0.
You can changed the 1's or 0's depending on what you want them to be. In your case, all zeros for outputs.

or
'add your stuff here'
trisC = %00000000

Main:
PORTC = %00001111
pause 1000
PORTC = %11110000
pause 1000
Goto Main

[comwarrior]

for tris, 0 is output and 1 is input