[SOLVED][g++] Strange behaviour within loops

Question

Hello
I've recently installed Arch64 on lappy. It will be used mostly for programming, therefore that's the thing which really makes me anxious: namely, loops doesn't work as they should. They seem to be skipping one iteration. As far as I have investigated, it happens when i use scanf.
Here's the code that doesn't work for me:
#include <cstdio>
using namespace std;
int main(int argc, char ** argv)
char tmp;
int index = 0;
do
printf("%d\n", index++);
printf("Enter char: ");
scanf("%c", &tmp);
printf("ASCII: %d\n", tmp);
while(tmp != '~');
return 0;
Here's what I get in terminal:
0
Enter char: l
ASCII: 108
1
Enter char: ASCII: 10
2
Enter char:
Step with number 1 is definitely not ok.
Some useful info:
glibc 2.11-1
gcc 4.4.2-3
Linux asus 2.6.31-ARCH #1 SMP PREEMPT Tue Nov 10 19:01:40 CET 2009 x86_64 Intel(R) Core(TM)2 Duo CPU T6600 @ 2.20GHz GenuineIntel GNU/Linux
Thanks in advance for telling me what I miss here.
Last edited by bfo (2009-11-28 15:03:33)

Answer 1

Trent wrote:
May I suggest that scanf is not what you want.  In fact, scanf is almost never what you want, as described here:
http://c-faq.com/stdio/scanfprobs.html
But your code is more C-like than C++-like (from what I understand; I know very little C++).  Surely there is a more idiomatic way to read characters from stdin in C++?  Perhaps someone can educate me.
This would work in C++ (not sure it is the easiest way though, but it's easy to read):
#include <iostream>
using namespace std;
int main(int argc, char* argv[]) {
char tmp;
int index = 0;
do {
cout << index++ << endl;
cout << "Enter char: ";
cin >> tmp;
cout << "ASCII: " << static_cast<int>(tmp) << endl;
} while (tmp != '~');
return 0;
cin ignores white space too, so you don't have to worry about things like '\n'.