Thread: how to fix this pattern code..

the presented above code is supposed to work

first i check if it starts with a number then i check if the returned char is "," then i check if i get number after it.
then i check if its the end '\0'

why its not working?

scanf() will *not* be terminated with anything, fgets() will be if room in the buffer, allows. iirc

Perhaps that's why Laserlight was suggesting getchar(), to pull the \n off the keyboard buffer. I have to say I haven't followed all of this drama.

Originally Posted by shoutatchickens

Am I wrong in thinking that user inputted text from stdin will not be null terminated. I am not really sure but maybe that is the problem?

User input, that is read in with %s, will be null terminated. User input, that is read in character by character, will be newline-terminated (which is what the above code assumes).

where is the mistake

Code:

#include <stdio.h>


int is_valid(const char *input);
const char *match_number(const char *input);
int main()
{
int i;
int ch;
int input[40];

   printf("enter string\n");
 for (i = 0; i < 39 && (ch = getchar()) != '\n' && ch != EOF; ++i)
    {
        input[i] = ch;
    }

    input[i] = '\0';

    if (is_valid(input))
    {
        printf("%s is valid.\n", input);
    }
    else
    {
        printf("%s is invalid.\n", input);
    }

    return 0;
}

/* Match one or more consecutive digits and return a pointer to the first char
 * that is not a digit.
 */
const char *match_number(const char *input)
{
    while((*input<='9')&&(*input>='0')){

     input++; //increasing the  address by1
    }

    return input;
}


int is_valid(const char *input)
{
  if (((*input)<'0')||((*input)>'9')){
		   return 0;
	   }
	   input=match_number(input);
  if (*input==','){
      
       if (((*input)<'0')||((*input)>'9')){
		   return 0;
	   }
      input=match_number(input+1);
      if (*input=='\0'){
       return 1;
      }
  }
  else
  {
   return 0;
  }
}

Code:

if (*input==','){
      /*Ten guesses as to what input is right here, first nine don't count */
     /*Ten guesses as to whether the next if-statement will be true, first nine don't count */
       if (((*input)<'0')||((*input)>'9')){
		   return 0;
	   }
      input=match_number(input+1);
      if (*input=='\0'){
       return 1;
      }

You still need to learn to read code as it is written, not as you wish it to be.

Originally Posted by tabstop

Code:

if (*input==','){
      /*Ten guesses as to what input is right here, first nine don't count */
     /*Ten guesses as to whether the next if-statement will be true, first nine don't count */
       if (((*input)<'0')||((*input)>'9')){
		   return 0;
	   }
      input=match_number(input+1);
      if (*input=='\0'){
       return 1;
      }

You still need to learn to read code as it is written, not as you wish it to be.

this is a part of a code i posted before
whats the mistake in it?

Originally Posted by transgalactic2

this is a part of a code i posted before
whats the mistake in it?

You've still got ten guesses left. (Although of course there's no need to guess, if you've got even .01 of a clue.)

i changed it so it will check *(input+1)

still bot working

Code:

#include <stdio.h>


int is_valid(const char *input);
const char *match_number(const char *input);
int main()
{
int i;
int ch;
int input[40];

   printf("enter string\n");
 for (i = 0; i < 39 && (ch = getchar()) != '\n' && ch != EOF; ++i)
    {
        input[i] = ch;
    }

    input[i] = '\0';

    if (is_valid(input))
    {
        printf("%s is valid.\n", input);
    }
    else
    {
        printf("%s is invalid.\n", input);
    }

    return 0;
}

/* Match one or more consecutive digits and return a pointer to the first char
 * that is not a digit.
 */
const char *match_number(const char *input)
{
    while((*input<='9')&&(*input>='0')){

     input++; //increasing the  address by1
    }

    return input;
}


int is_valid(const char *input)
{
  if (((*input)<'0')||((*input)>'9')){
		   return 0;
	   }
	   input=match_number(input);
  if (*input==','){
        if (((*(input+1))<'0')||((*(input+1))>'9')){
		   return 0;
	   }
      input=match_number(input+1);
      if (*input=='\0'){
       return 1;
      }
  }
  else
  {
   return 0;
  }
}

Of course it doesn't work.

Code:

$ ./numbers
enter string
2,1
2,1 is valid.

(Hint: input is an array of chars, not an array of ints.)

i am not using it as an int array

in every line its being used as a char array

Originally Posted by transgalactic2

i am not using it as an int array

in every line its being used as a char array

Originally Posted by transgalactic2

i changed it so it will check *(input+1)

still bot working

Code:

#include <stdio.h>


int is_valid(const char *input);
const char *match_number(const char *input);
int main()
{
int i;
int ch;
int input[40];
/* et cetera */

Want to try that again?

I changed that
but "2,1" is valid

but this input "2,1 " should be invalid

in the end it checks if it equals '\0'
why its saying "2,1 " is valid??

Code:

#include <stdio.h>


int is_valid(const char *input);
const char *match_number(const char *input);
int main()
{
int i;
int ch;
char input[40];

   printf("enter string\n");
 for (i = 0; i < 39 && (ch = getchar()) != '\n' && ch != EOF; ++i)
    {
        input[i] = ch;
    }

    input[i] = '\0';

    if (is_valid(input))
    {
        printf("%s is valid.\n", input);
    }
    else
    {
        printf("%s is invalid.\n", input);
    }

    return 0;
}

/* Match one or more consecutive digits and return a pointer to the first char
 * that is not a digit.
 */
const char *match_number(const char *input)
{
    while((*input<='9')&&(*input>='0')){

     input++; //increasing the  address by1
    }

    return input;
}


int is_valid(const char *input)
{
  if (((*input)<'0')||((*input)>'9')){
		   return 0;
	   }
	   input=match_number(input);
  if (*input==','){
        if (((*(input+1))<'0')||((*(input+1))>'9')){
		   return 0;
	   }
      input=match_number(input+1);
      if (*input=='\0'){
       return 1;
      }
  }
  else
  {
   return 0;
  }
}

So I've been assuming you've been reading the messages from your compiler, but that's probably an unwise assumption. So the compiler says this:

Code:

$ gcc -Wall -Wextra -o numbers numbers.c
numbers.c: In function ‘is_valid’:
numbers.c:66: warning: control reaches end of non-void function

because there is one way to get "no answer" out of your is_valid function, namely when you have spaces (or other characters) at the end of the input. So remember: every path must have a return value -- find the if with no else, and fix it.

thanks i forgot to mention the else case in '\0' if