Thread: Exit a function

here's what i have...

Code:

void header (void)
{
printf("Enter the year (21st century): ");/*Asks user for the year*/
    		scanf("%d",&year);
    	if (year > 2100 || year < 2001) /*if not a valid year give error*/
		{
			printf ("Calendar unavailable for invalid years.\n");/*print error*/
			exit(0);
		}
}

its followed by another input function...i want to exit this function and stop the program if its not a valid year...i used exit (0); but it gives a warning .. of warning C4013: 'exit' undefined; assuming extern returning int ....i just want to exit and not continue if the condition is true...