Ben voilà, tout est dans le titre ...

sous quel os ?
 
sous win , fonct° de l api win.
 
ex : ExitWindowsEx(EWX_REBOOT , 0)
 
Platforms: Win 95/98, Win NT  
 
ExitWindowsEx shuts down or reboots the user's computer. Of course, since the shutdown/reboot process will begin once the function is called, there won't normally be much left for your program to do. The function returns 0 if an error occured, or 1 if successful.  
 
uFlags
One or more of the following flags specifying how to shut down or reboot the computer:  
EWX_FORCE = 4
Force any applications to quit instead of prompting the user to close them.  
EWX_LOGOFF = 0
Log off the network.  
EWX_POWEROFF = 8
Shut down the system and, if possible, turn the computer off.  
EWX_REBOOT = 2
Perform a full reboot of the system.  
EWX_SHUTDOWN = 1
Shut down the system.  
dwReserved

Ouais c'étais pour windows, déoloé de n'avoir pas précisé...
Merci beaucoup.