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pointers problem

 
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art



Joined: 21 May 2015
Posts: 181

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pointers problem
PostPosted: Wed Jun 10, 2015 8:07 am     Reply with quote
Hi,
I have problem with pointers. When I type 1234, B0,B1,B2 and B3 will become high, but if after that i send command 0, B0,B1,B2 and B3 still High. What is wrong with my coding? suppose all port B become low when i send command 0.

Code:

#include <18F452.h>
#device PASS_STRINGS=IN_RAM
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(crystal=20MHz)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

#include <stdio.h>
#include <input.c>
#include <string.h>

void main()
{
char *ptr;
char arrayChars[10];
   
ptr=arrayChars;

while(true)
  {
   printf("Enter number : %s \n",arrayChars);
   get_string(arrayChars,10);

   for(ptr=1;ptr<5;ptr++)
     {
      if (strcmp(arrayChars, "0" )==0)
          output_B(0b00000000);
         
      if (*ptr=="1")
          output_high(PIN_B0);
      if (*ptr=="2")
          output_high(PIN_B1);
      if (*ptr=="3")
          output_high(PIN_B2);
      if (*ptr=="4")
          output_high(PIN_B3);
     }
  }
}
rikotech8



Joined: 10 Dec 2011
Posts: 376
Location: Sofiq,Bulgariq

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PostPosted: Wed Jun 10, 2015 8:55 am     Reply with quote
You compare a char with string *ptr == "1"
"1" is set of two characters '1' and '\0'-string terminator.

Try to enclose 1 in single quotation marks to tell the compiler its type is a single char.

(*ptr=='1')

Another thing that may help is to clear the array arrayChars right above get string function.
Code:
strcpy(arrayChars, "");


I hope this will help
_________________
A person who never made a mistake never tried anything new.
Ttelmah



Joined: 11 Mar 2010
Posts: 19515

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PostPosted: Wed Jun 10, 2015 9:05 am     Reply with quote
There are two separate problems.

First when you declare 'arrayChars', it is not initialised. It could initially contain _anything_, and almost certainly will not contain a terminating '\0'. The first print then could easily result in garbage being displayed.

Then the second problem is that '==' will not compare a _string_. It can compare a character, but your right hand argument is a string. I see Rokotech8, has spotted the same problems, while I was on the phone and typing.
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Wed Jun 10, 2015 9:14 am     Reply with quote
One more very bad problem. Below, you declare 'ptr' as a char pointer
and initialize it to point to arrayChars[].
Quote:
char *ptr;
char arrayChars[10];

ptr=arrayChars;


But then, you use 'ptr' in a for() loop, wiping out the address of
arrayChars which was stored in it:
Quote:

for(ptr=1;ptr<5;ptr++)
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