How to exit a while loop with a keystroke in C? - c++

Question

I want to have user press the space key to jump out of the while loop.
For example:
while ( some condition )
{
printf ("Press space bar to continue...");
}
Thanks!!

Answer 1

I think you mean the following as long as a spacebar followed by the enter key is acceptable given your comments above.
char input = 0;
while( input != ' ' )
{
printf("Press space bar to continue...\n");
scanf("%c",&input);
}
Or if you prefer, without hitting the enter key:
#include <stdio.h>
int main(int argc, char **argv)
{
char input = 0;
while( input != ' ' )
{
printf("Press space bar to continue...\n");
input = getch();
}
}
This worked on my msysgit bash shell. BUT, some people will insist that it work on Linux as well. Which is fine I guess, I love Linux, but I said the above solution worked on msysgit. The following works on my, let me be specific, Oracle VM for Ubuntu 10.10.
#include <stdio.h>
#include <termios.h>
#include <unistd.h>
int main(int argc, char **argv)
{
char input = 0;
while( input != ' ' )
{
printf("Press space bar to continue...\n");
input = mygetch();
}
}
int mygetch(void)
{
struct termios oldt, newt;
int ch;
tcgetattr( STDIN_FILENO, &oldt );
newt = oldt;
newt.c_lflag &= ~( ICANON | ECHO );
tcsetattr( STDIN_FILENO, TCSANOW, &newt );
ch = getchar();
tcsetattr( STDIN_FILENO, TCSANOW, &oldt );
return ch;
}
The mygetch came from here.

Answer 2

Capturing keystrokes under most platforms requires you to access the console directly. Typically there are libraries available to help you with that. Low-level libraries are termcap (which is derived from terminal capabilities) libraries. There is a "portable" layer on top of termcap called curses. Linux uses the GNU version which is called ncurses and is actually available on a multitude of platforms.
Curses is extensively documented, you can start a tutorial using
$ man ncurses
Your problem requires steps to initialize the console and set up keystroke reader. There are several ways to achieve your desired effect.
I am posting a working example for you to play with. It shows some basic ideas in curses:
/* file: curses_ex1.c */
#include <stdio.h>
#include <curses.h>
const char rotary[4] = "/-\\|";
int main() {
WINDOW *w;
int i = 0;
w = initscr();
if ( w == NULL ) {
return -1; /* unable to initialize curses */
}
timeout(500); /* do not block */
mvprintw(0, 0, "Press space bar to break out of the loop.");
noecho();
for(i = 0; ; i++) { /* no condition so loops forever */
int c;
mvaddch(0, 42, rotary[i%4]); /* display rotator */
c = getch(); /* get a character */
if ( c == ' ')
break;
if ( c != ERR ) { /* not a space but another valid key */
mvprintw(1, 0, "You need to press a space for me to stop (you pressed `%c')", c);
}
}
endwin();
return 0;
}
To compile it:
cc -o curses_ex1 curses_ex1.c -lcurses

Answer 3

Make a variable x = 1, put that in the condition, when they press space bar, set x to 2.