Below is some code that posts a "c" character event. The event codes are in <HIToolbox/Events.h>. If you're looking to target event posts to a specific process (as opposed to globally in the sample below), you should use the CGEventPostToPSN() function instead.
CGEventSourceRef eventSource = CGEventSourceCreate(kCGEventSourceStateCombinedSessionState);
if (eventSource != NULL) {
CGEventRef eventDown = CGEventCreateKeyboardEvent(eventSource, (CGKeyCode)0x08, YES);
CGEventPost(kCGSessionEventTap, eventDown);
CFRelease(eventDown);
CGEventRef eventUp = CGEventCreateKeyboardEvent(eventSource, (CGKeyCode)0x08, NO);
CGEventPost(kCGSessionEventTap, eventUp);
CFRelease(eventUp);
CFRelease(eventSource);
}