Code:
#include <stdio.h>

int menu(void);
void hellofunc(void);
void goodbyefunc(void);

int main(void)
{
	int choice;
	while ((choice = menu()) != 3) {
		switch (choice) {
			case 1: hellofunc(); break;
			case 2: goodbyefunc(); break;
			default: printf("Invalid choice.\n");
		}
	}

	return 0;
}

int menu(void)
{
	int choice;
	printf("\n\nMenu\n");
	printf("1. Say hello.\n");
	printf("2. Say goodbye.\n");
	printf("3. Quit.\n>");

	scanf("%d",&choice);
	return choice;
}

void hellofunc(void)
{
	printf("Hello there.");
}

void goodbyefunc(void)
{
	printf("Goodbye, sir.");
}
or something like that.