Adding using getchr()

Observations:

- This program is a state machine. The use of result and tempval gives you an ad hoc sort of state, but it would be more clear to simply have an explicit state variable.

- You can use character literals ('X') instead of numeric ones (0x58) for clarity. Most likely you should define constants for even better readability.

- Take a look at the standard library function isdigit(), and some of its friends like isupper() if case sensitivity is an issue.

- When you clear X upon detecting a Z, you destroy the sum you've accumulated by assigning 0. Presumably you wanted the sum for a reason.

- There's a perfectly good getchar() already implemented. What's the mask to 7 bits for? Are you worried about parity? Or just being really finicky about your definition of ASCII?

- Are you sure you want the sum of the single digits, as ASCII, between the X and Z, and not the value of the integer delimited by those characters? That is, if you get X123Z, you want the result to be 6, and not 123?

- What happens if the input isn't well formed, and you get some other input (from line noise or whatever)?

typedef enum
    {
    Idle,
    SummingDigits
    } InputState;

InputState state;

#define  SequenceStart   'X'
#define  SequenceEnd     'Z'

void main (void)
    {
    char c;
    int sum;

    state = Idle;

    for (;;)
        {
        c = getchr();

        switch (state)
            {
            case Idle :
                if (c == SequenceStart)
                    {
                    sum = 0;
                    state = SummingDigits;
                    }
                // else bad input; ignore
                break;

            case SummingDigits :
                if (c == SequenceEnd)
                   {
                   state = Idle;
                   // probably want to do something with sum here
                   }
                else if (isdigit(c))
                   {
                   sum += c - '0';
                   }
                // else bad input
                break;

            } // switch state

        } // loop forever

    } // main

I would like to say thank you for your help first. But I still have the same result. In your program like mine the sum keeps on adding up even when a key isn't pressed. If you run the program and look on the serial window you'll see that the result count keeps on adding up. I hope It not my age kicking in HA HA.

#include <reg51.h>
#include <stdio.h>
#include <ctype.h>

unsigned int getchr(void);

typedef enum
{
Idle,
SummingDigits
} InputState;

InputState state;

#define SequenceStart 'X'
#define SequenceEnd 'Z'

void main (void)
{
char c;
int sum;


SCON = 0x50;
TMOD = 0x20;
TH1 = 0xFD; //9600 baud
TR1 = 1;
TI = 1;

state = Idle;

for (;;)
{
c = getchr();

switch (state)
{
case Idle :
if (c == SequenceStart)
{
sum = 0;
state = SummingDigits;
}
// else bad input; ignore
break;

case SummingDigits :
if (c == SequenceEnd)
{
state = Idle;
printf ("\rIdle=: %ld ",((unsigned long) sum));
}

else if (isdigit(c))
{
sum += c - '0';

printf ("\rProssing count=: %ld",((unsigned long) sum));
}
// else bad input
break;

} // switch state

} // loop forever

} // main


unsigned int getchr(void)
{
unsigned int chr;
chr = SBUF;
RI = 0;
return(chr);
}

I was under the (perhaps subconcious) impression that getchr() would block until a character was available. But looking at your second implementation, it clearly doesn't wait.

Depending on your goals, you probably want getchr() to wait for RI to become 1 (signalling a new character) before returning, in which case this problem should go away. Compare with Keil's implementation of getkey():

unsigned int getchr(void)
    {
    unsigned int chr;
    chr = SBUF;
    RI = 0;
    return(chr);
    }

char _getkey ()  {
  char c;

  while (!RI);
  c = SBUF;
  RI = 0;
  return (c);
}

Thank you for your help! I knew I was over looking something and that was the while (!RI);

Thank you again,
Glenn