Getchar() Doesn't Work on Conditional Control Statement

[windscar]

Hello Everybody!

I am a beginner that try to learn C++ programming. I work in Linux Ubuntu Karmic Koala (9.10) environment.

I got a problem with getchar(). The function works well in a simple program. But when I use it in while (cond.) and switch (var.) , the function doesn't work, it doesn't even ask me to input character (including "\n"). Or maybe there are other reasons why getchar() doesn't work.

I am sorry if I repost the same question. But I already searched on Internet but I still can't find the answer. So I decided to ask this problem to this forum.

Here the code:

#include <ncurses.h>
#include <iostream>
	using namespace std;
#include <stdlib.h>

void menu();

int main() {
	int stop(0);
	int choice;
	
	while (stop == 0) {
		menu();
		cout << "Input: ";
		cin >> choice;
		switch (choice) {
			case 1  : cout << "press any key ...";
				  getchar();
				  cout << endl << endl;
				  break;
			case 2  : stop = 1;
				  break;
			default : cout << "Prompt Error..." << endl << endl;
				  break;
		}
	}
	return 0;
}

void menu () {
	cout << "Menu: \n";
	cout << "1. Keep looping" << endl;
	cout << "2. Stop and quit" << endl;
}

Can somebody help me and explain why getchar() doesn't work?

Thank you,
Wind Scar

[olredixsis]

use _getch() not getchar().

[olredixsis]

use _getch() for C++ and getch() for C, not getchar().

[unoriginal]

getch() is non-standard and _getch() is even less so. Avoid using conio.h as far as possible.

Let me explain why your getchar() isn't working. That is because you use cin at line 15. When you input a number a newline along with the number will also be read. So, the getchar() reads the newline and hence your program never pauses.

Precede your getchar() call by a fflush() call to flush out unwanted newlines or any other char. Like this: fflush(stdin);

That is all, and your getchar() will then work as you expect it to. However, you may want to change the "Pressy any key" to "Press ENTER".

[windscar]

@ Dear olredixsis,
I work on Linux Ubuntu Karmic Koala (9.10), so _getch() won't be recognized by its compiler (g++) because Linux doesn't have conio.h. I already mentioned it, didn't I? Anyway, thank you for trying to help me :)

@ Dear unoriginal,
Thank you for your explanation. But it still doesn't work as I expect it. I add fflush(stdin) like you said, and my code becomes like this:

#include <ncurses.h>
#include <iostream>
	using namespace std;
#include <stdlib.h>

void menu();

int main() {
	int stop(0);
	int choice;
	
	while (stop == 0) {
		menu();
		cout << "Input: ";
		cin >> choice;
		switch (choice) {
			case 1  : cout << "press ENTER ...";
				  fflush(stdin);
				  getchar();
				  cout << endl << endl;
				  break;
			case 2  : stop = 1;
				  break;
			default : cout << "Prompt Error..." << endl << endl;
				  break;
		}
	}
	return 0;
}

void menu () {
	cout << "Menu: \n";
	cout << "1. Keep looping" << endl;
	cout << "2. Stop and quit" << endl;
}

Are my codes written incorrectly?

[Computergeek01]

Move the fflush(stdin) to line 16 and try that, right now fflush() is only occuring when case 1 = true.

[windscar]

@ Dear Computergeek01,
Thank you for trying to help me. I already tried your advice. But it still doesn't work. I put fflush(stdin) on line 16 (below cin >> choice). My code becomes like this:

#include <ncurses.h>
#include <iostream>
	using namespace std;
#include <stdlib.h>

void menu();

int main() {
	int stop(0);
	int choice;
	
	while (stop == 0) {
		menu();
		cout << "Input: ";
		cin >> choice;
		fflush(stdin);
		switch (choice) {
			case 1  : cout << "press ENTER ...";
				  getchar();
				  cout << endl << endl;
				  break;
			case 2  : stop = 1;
				  break;
			default : cout << "Prompt Error..." << endl << endl;
				  break;
		}
	}
	return 0;
}

void menu () {
	cout << "Menu: \n";
	cout << "1. Keep looping" << endl;
	cout << "2. Stop and quit" << endl;
}

Did I make a mistake?

[windscar]

Hello everybody,

Finally with some experiments, I can make the getchar() works as my expectation. By putting getchar() and cin.get() together. So, my code becomes like this:

#include <ncurses.h>
#include <iostream>
	using namespace std;
#include <stdlib.h>

void menu();

int main() {
	int stop(0);
	int choice;
	
	while (stop == 0) {
		menu();
		cout << "Input: ";
		cin >> choice;
		switch (choice) {
			case 1  : cout << "press ENTER ...";
				  getchar();
				  cin.get();
				  cout << endl << endl;
				  break;
			case 2  : stop = 1;
				  break;
			default : cout << "Prompt Error..." << endl << endl;
				  break;
		}
	}
	return 0;
}

void menu () {
	cout << "Menu: \n";
	cout << "1. Keep looping" << endl;
	cout << "2. Stop and quit" << endl;
}

It does work! Anyway, if you have other better solutions, I'll appreciate it if you share it :)
(notice on line 18 and 19...)

[Zhuge]

fflush(stdin); is bad.

http://www.cprogramming.com/faq/cgi-bin/smartfaq.cgi?answer=1052863818&id=1043284351

[windscar]

@ Dear Zhuge,

Thank you for your nice information :)