/*
 * File: menu.c
 * Description: simple menu implementation to demo flush problem
 * Author: pcyu16
 * Last update: 2010/12/31 20:35
 *
 * expected result: input 2 numbers, then print a menu,
 *                  ask for output destination, then deal with user input option
 * actually result: after input 2 numbers, program exit with error message predefined
 */
#include <stdio.h>
#include <stdlib.h>

int main()
{
	int a, b;
	FILE *fout;

	// title
	puts("The A+B Problem");

	// read numbers
	printf("please input a b >> ");
	scanf("%d %d", &a, &b);

	// menu
	puts("a. output to standard output");
	puts("b. output to out.txt");
	printf("\n>> ");
	fflush(stdout);

	int option;

	option = getchar();

	// seletion statment by option read
	if(option == 'a')
		fout = stdout;
	else if(option == 'b')
		fout = fopen("out.txt", "w");
	else{
		// printf("key value: %d\n", option);
		fprintf(stderr, "ERROR! INVALID OPTION!!\n");
		exit(1);
	}

	// output calculated result
	fprintf(fout, "%d + %d = %d\n", a, b, a+b);
	return 0;
}