Strange keyboard??

I´m trying to write a program that can handle different keypresses. I´ve downloaded an ASCII table so I know what value each key has http://www.asciitable.com.

If I understand it right there is two different versions of ASCII tabel, one "usual" (0-127) and one extended (0-255). Im using the getch() function and it works well on "alfabetic"(visible) character but when I retreive a value from leftarrow I get a negative value (-32). Is it possible (apperntly it is) to get a negative value?? But what is more strange is that I get the same value for left/right/up/down arrow (-32).

Simple code

Code:

---

int main()
{
        char ch;
                ch = getch();
                printf(" %d", ch);
return 0;
}

---

Shouldn´t each key return a different value???

A char is unsigned. So a -32 is really 224. Some keys, namely the arrow keys and function keys, return two values. The first number is an escape code (for F1-F10 it's char(0) and for F11, F12, and the arrow keys it's char(224)) and the second number is the actual key value.

Code:

---

int main()
{
        char ch;

        do
        {
                ch = getch();
                printf(" %d", ch);
        } while (ch != 27);        // loop until press escape

        return 0;
}

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Try this code. When you press the left arrow key you should get 224 and 75.

Whoops. Cast the char into an unsigned integer.

printf(" %d", unsigned int (ch));

I just toyed with this same issue not long ago. I never got an absolute confirmation that this would cause random errors, but it traps function and arrow keys.

Code:

---


unsigned key1, key2;

do
{
    key1 = getch();
    if(key1 == 0)
    {
          key2 = getch();
          switch(key2)
          {
                case 72  /*up arrow */
                and so on
          };
      }
      else
    {
     
          switch(key1)
          {
            do whatever here.
            printf("%c", key1);
        };
      }
}while(sentinel == true);

---

Code:

---

#include <stdio.h>
#include <conio.h>

main()
{
        char c;
       
        printf("KEY\tCODE\n");

        while ((c = getch()) != 27) //as long as 'Esc' is not pressed
        {
                printf("%3c\t%4d\n", c, (int) c);
        }
}

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