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Sep 23rd, 2006

Re: How do you check if arrow keys are pressed?

Click to Expand / Collapse Quote originally posted by Diode ...

What is the top decimal value that kbhit() catches when you hit a key? I didn't know about kbhit. So I coded the entire thing from scratch. It works. But the UP arrow key for example is " H", that is: NULL, capital h. It is actually 2 characters. Does kbhit() catch 2 characters? And could you provide a sample program that prints on the screen that an arrow key was hit, like I coded my sample program? I am curious about this apparent quick way that you provided.

kbhit() doesn't catch characters. It returns TRUE if a key has been pressed, FALSE if no key is waiting. That way your program can do whatever processing it needs and not wait for a key. In effect it makes the keyboard interrupt driven. Leave out the kbhit() call if you don't need to test for keyboard readyness.

As for a sample program, just output the value of the integers ch1 and ch2.

WaltP

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Sep 26th, 2006

Re: How do you check if arrow keys are pressed?

Okay, so what libraries are getch() and kbhit() included in? (I think I might test this one out, after I reformat my computer...)

Last edited by FireSBurnsmuP; Sep 26th, 2006 at 1:31 am. Reason: needed different tone

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Sep 26th, 2006

Re: How do you check if arrow keys are pressed?

Click to Expand / Collapse Quote originally posted by FireSBurnsmuP ...

Okay, so what libraries are getch() and kbhit() included in? (I think I might test this one out, after I reformat my computer...)

In conio.h but this is not standard so there are posibility that you don't have this library.

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Oct 31st, 2006

Re: How do you check if arrow keys are pressed?

diode, I ran your code in Dev-C++, and I found one error, last: didn't have anything happen, so I put in a nonsense integer declaration.

Also, when I ran it, if I press an arrow key, it displays a lowercase alpha, then the letter you defined. It doesn't detect that an arrow key was pressed (it doesn't say, "You pressed the [insert key here] key!"). I don't know, maybe Dev-C++ does something different. I haven't attempted to look through all of the code yet; it's a little late (early?) and I am not that great at C++ yet.
[EDIT] Wait! you used a lot of c libraries, no wonder, I haven't dealt with those at all... [/EDIT]

Anyways, I was hoping maybe you could explain this error I encountered.

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Sep 2nd, 2008

Re: How do you check if arrow keys are pressed?

Click to Expand / Collapse Quote originally posted by FireSBurnsmuP ...

diode, I ran your code in Dev-C++, and I found one error, last: didn't have anything happen, so I put in a nonsense integer declaration.

Also, when I ran it, if I press an arrow key, it displays a lowercase alpha, then the letter you defined. It doesn't detect that an arrow key was pressed (it doesn't say, "You pressed the [insert key here] key!"). I don't know, maybe Dev-C++ does something different. I haven't attempted to look through all of the code yet; it's a little late (early?) and I am not that great at C++ yet.
[EDIT] Wait! you used a lot of c libraries, no wonder, I haven't dealt with those at all... [/EDIT]

Anyways, I was hoping maybe you could explain this error I encountered.

Sorry, I just now found your reply. I haven't messed with this program for a long time. In fact, I forgot all about it. I've moved on to working with (as much as possible) ANSI standard C, and now I am moving onto C++. Sorry if I wasn't more help.

BTW, about your sig, I didn't know Ozzy Osbourne said that, but that is also on a Magic: the Gathering card, though I forget which one.

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Dec 21st, 2008

Re: How do you check if arrow keys are pressed?

Click to Expand / Collapse Quote originally posted by WaltP ...

I usually do it with this:
C Syntax (Toggle Plain Text)
if (kbhit())
{
    ch1 = getch();
    if (ch1 != '\0')
    {
            // process a normal keystroke
    }
    else
    {
        ch2 = getch();    // get the arrow or function key
        switch(ch2)
        {
                // process the arrow or function key
        }
    }
}
if (kbhit()) { ch1 = getch(); if (ch1 != '\0') { // process a normal keystroke } else { ch2 = getch(); // get the arrow or function key switch(ch2) { // process the arrow or function key } } }
You can use this to discover what the key values are.

This only works for compilers that have getch() and kbhit() defined, of course.

please explain your code

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Dec 21st, 2008

Re: How do you check if arrow keys are pressed?

Click to Expand / Collapse Quote originally posted by chandangang ...

please explain your code

getch() returns 0 when one of the special keys is pressed, such as one of the Function or arrow keys. When that happens the program has to call getch() again which will return the key code of the key that was pressed. The reason for this behavior is that special keys have the same key codes as other normal keys, and the program needs some way to distinguish them. When I write such programs I normally make those key codes negative values so that the rest of the program can easily distintuish between normal and special keys. Other programmers have added 255 to the value, which works ok too.

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Dec 23rd, 2008

Re: How do you check if arrow keys are pressed?

thanx

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Feb 5th, 2010

-1

Re: How do you check if arrow keys are pressed?

****(1)*****

C Syntax (Toggle Plain Text)
#include<stdio.h>
#include<conio.h>
 
void main()
{
char c;
clrscr();
printf("Press \"Esc\" to exit");
gotoxy(1,10);
c=getch();
 while(c!=27)
 {
  if(c==0)
  {
  c=getch();
  gotoxy(1,10);
  clreol();
  printf("This key has two ascii values: 0 and %d",c);
  }
  else
  {
  gotoxy(1,10);
  clreol();
  printf("%d",c);
  }
 c=getch();
 }
}
#include<stdio.h>
#include<conio.h>

void main()
{
char c;
clrscr();
printf("Press \"Esc\" to exit");
gotoxy(1,10);
c=getch();
 while(c!=27)
 {
  if(c==0)
  {
  c=getch();
  gotoxy(1,10);
  clreol();
  printf("This key has two ascii values: 0 and %d",c);
  }
  else
  {
  gotoxy(1,10);
  clreol();
  printf("%d",c);
  }
 c=getch();
 }
}

************

*****(2)******

C Syntax (Toggle Plain Text)
#include<stdio.h>
#include<conio.h>
 
void main()
{
char c;
int x=1,y=1;
clrscr();
for(y=1;y<17;y++)
{
gotoxy(52,y);
printf("|");
}
gotoxy(1,16);
printf("___________________________________________________/");
gotoxy(1,19);
printf("Press \"Esc\" to exit\n\n");
printf("Use arrow keys to move cursor");
x=1;
y=1;
gotoxy(x,y);
c=getch();
 while(c!=27)
 {
  if(c==0)
  {
  c=getch();
   if(c==77)
   {
    if(x==51)
    {
    x=1;
    gotoxy(x,y);
    }
    else
    {
    x++;
    gotoxy(x,y);
    }
   }
 
   if(c==75)
   {
    if(x==1)
    {
    x=51;
    gotoxy(x,y);
    }
    else
    {
    x--;
    gotoxy(x,y);
    }
   }
 
   if(c==80)
   {
    if(y==15)
    {
    y=1;
    gotoxy(x,y);
    }
    else
    {
    y++;
    gotoxy(x,y);
    }
   }
 
   if(c==72)
   {
    if(y==1)
    {
    y=15;
    gotoxy(x,y);
    }
    else
    {
    y--;
    gotoxy(x,y);
    }
   }
  }
 
  else if(c==8)
  {
   if(x==1)
   {
   x=51;
   gotoxy(x,y);
   }
   else
   {
   x--;
   gotoxy(x,y);
   }
  }
 
  else
  {
   if(x==51)
   {
    if(y==15)
    {
    y--;
    }
   x=x-50;
   y++;
   gotoxy(x,y);
   }
   else
   {
   printf("%c",c);
   x++;
   }
  }
 c=getch();
 }
}
#include<stdio.h>
#include<conio.h>

void main()
{
char c;
int x=1,y=1;
clrscr();
for(y=1;y<17;y++)
{
gotoxy(52,y);
printf("|");
}
gotoxy(1,16);
printf("___________________________________________________/");
gotoxy(1,19);
printf("Press \"Esc\" to exit\n\n");
printf("Use arrow keys to move cursor");
x=1;
y=1;
gotoxy(x,y);
c=getch();
 while(c!=27)
 {
  if(c==0)
  {
  c=getch();
   if(c==77)
   {
    if(x==51)
    {
    x=1;
    gotoxy(x,y);
    }
    else
    {
    x++;
    gotoxy(x,y);
    }
   }

   if(c==75)
   {
    if(x==1)
    {
    x=51;
    gotoxy(x,y);
    }
    else
    {
    x--;
    gotoxy(x,y);
    }
   }

   if(c==80)
   {
    if(y==15)
    {
    y=1;
    gotoxy(x,y);
    }
    else
    {
    y++;
    gotoxy(x,y);
    }
   }

   if(c==72)
   {
    if(y==1)
    {
    y=15;
    gotoxy(x,y);
    }
    else
    {
    y--;
    gotoxy(x,y);
    }
   }
  }

  else if(c==8)
  {
   if(x==1)
   {
   x=51;
   gotoxy(x,y);
   }
   else
   {
   x--;
   gotoxy(x,y);
   }
  }

  else
  {
   if(x==51)
   {
    if(y==15)
    {
    y--;
    }
   x=x-50;
   y++;
   gotoxy(x,y);
   }
   else
   {
   printf("%c",c);
   x++;
   }
  }
 c=getch();
 }
}

************

Compiler: Borland's Turbo C++ (Version 3.0)

Special keys(arrow keys,function keys,delete,home,page up,end,....etc) have ascii values but
they have TWO ascii values, and thats why we have to use getch() TWICE
to sense them.
I have NOT used kbhit(), but I got the idea of using getch()
TWICE for special keys from WaltP's post, Thanx WaltP.

Last edited by hsp700; Feb 5th, 2010 at 7:33 am.

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Feb 5th, 2010

Re: How do you check if arrow keys are pressed?

Add.......

C Syntax (Toggle Plain Text)
else if(c==13)
  {
  gotoxy(x,y);
  }
else if(c==13)
  {
  gotoxy(x,y);
  }

****(2)*****

C Syntax (Toggle Plain Text)
void main()
{
...
...
while(c!=27)
{
  if(c==0)
  {
  }
 
  else if(c==8)
 {
 }
 
 >> H E R E <<
 
 else
 {
 }
c=getch();
}
}
void main()
{
...
...
while(c!=27)
{
  if(c==0)
  {
  }

  else if(c==8)
 {
 }

 >> H E R E <<

 else
 {
 }
c=getch();
}
}

...before running the code, Thank you.

Last edited by hsp700; Feb 5th, 2010 at 9:01 am.

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