how to fix this pattern code..

**~~transgalactic2~~** · 12-27-2008

I wrote a program which recognizes the following pattern
(num,num) (num,num) (num,num)

num is an integer number.

I took a copy of the input array to temp array.
then i changed temp like this:
first i transformed every space char ' ' into '' (no char)
then i transformed ever number before ',' to 4 and after ',' to 5 .
so my legal input should look like (4,5) (4,5) (4,5)
then if the char in the loop is ( it should expect 4,5)
if the char is 4 it should expect ,5) after it and ) before it

There are five terms to be completed each cycle
if the counter%5 =0 then the input is legal.

i wrote this code but as i showed in the code by comments it has errors
how to fix them?

Code:

#include <stdio.h>

int check_if_legal(char mines[],int length);
int main() {
        int index;
    char str[40];
    int i;
    int length;

 printf("enter length\n");
 scanf("%d",&length);
 printf("enter string\n");
 for(index=0;index<length;index++){
   scanf("%c",&str[index]); //13
 }
 i=getchar();

 printf("%d",check_if_legal(str,length));
return 0;
}

int check_if_legal(char mines[],int length)
{
    int state=-1;
    int counter=0;
    int flag_o=0;
    int flag_failure=0;
    int flag_z=0;
    int index2;
    int index;
    char temp[40];

for(index=0;index<length;index++){
   temp[index]=mines[index]; //13
 }

     for (index=0;index<length;index++){
         if (temp[index]==' '){      
             temp[index]='';   ////|39|empty character constant|

             if ((temp[index]<='9')&&(temp[index]=>'0')){ //|41|error: syntax error before '>' token|
                 temp[index]='4';
                 if (temp[index-1]=','){
                    temp[index]='5';
                 }
                 index2=index+1;
                 while((temp[index2]<='9')&&(temp[index2]=>'0')){//|47|error: syntax error before '>' token|
                      temp[index2]=''; //|48|empty character constant|
                     index2++;
                 }//end while
             }//end if
         }//end if
     }//end for
              for (index=0;index<length;index++){  // (4,5)

                if(temp[index]=='('){

                    if((temp[index+1]=='4')&&(temp[index+2]==',')&&(temp[index+3]=='5')&&(temp[index+4]==')')){

                         counter++;
                     }
                     else
                     {
                     state=1;
                     }
                }

                if(temp[index]=='4'){

                   if((temp[index-1]=='(')&&(temp[index+1]==',')&&(temp[index+2]=='5')&&(temp[index+3]==')')){

                                 counter++;
                     }
                     else
                     {
                     state=0;
                     }

                }

                if((temp[index]==','){

                     if((temp[index-1]=='4')&&(temp[index-2]=='(')&&(temp[index+1]=='5')&&(temp[index+2]==')')){

                                 counter++;
                     }
                     else
                     {
                     state=0;
                     }

                }
                if((temp[index]=='5')){

                 if((temp[index-3]=='(')&&(temp[index-1]==',')&&(temp[index-2]=='4')&&(temp[index+1]==')')){

                                  counter++;
                     }
                     else
                     {
                     state=0;
                     }

                }
                if((temp[index]==')'){

                    if((temp[index-1]=='5')&&(temp[index-2]==',')&&(temp[index-3]=='4')&&(temp[index-4]==')')){

                                  counter++;
                     }
                     else
                     {
                     state=0;
                     }

                }
               }//end for
               if ((counter>0)&&(counter%5==0){

                state=1;
               }

     return state;
 }//end func

**dwks** · 12-27-2008

Post the errors you're getting. I did notice that you have too many opening parentheses here and elsewhere:

Code:

if((temp[index]==')'){

Code:

temp[index]='';   ////|39|empty character constant|

You can't really have an empty character constant like that. I think perhaps you want to shift all of the characters to the right of temp[index] left one index, so that you effectively overwrite temp[index]. You can do this quite easily with memmove(), or implement it yourself.

**~~transgalactic2~~** · 12-27-2008

i posted each error as a comment near the line

i am pretty sure i could replace ' ' with '' i have done it in java

**laserlight** · 12-27-2008

Originally Posted by transgalactic2

i am pretty sure i could replace ' ' with '' i have done it in java

I am pretty sure that Java is not C and C is not Java. As you pointed out, the error message is right there: "empty character constant".

Actually, Java does not allow empty character literals either. You might be thinking of empty strings, which both C and Java allow, except that the C version would consist of a null character as the first character.

**~~transgalactic2~~** · 12-27-2008

so how to replace ' ' to an empty char
??

**~~transgalactic2~~** · 12-27-2008

so it will put the next char instead of it?

**laserlight** · 12-27-2008

Let's start from scratch. You want to check if user input matches this pattern: (num,num) (num,num) (num,num).

First, does this mean that num is always the same, e.g., you will accept (2,2) (2,2), (2,2) but reject (1,2) (3,4) (5,6)?

Now, the first step that I would take is to write code that matches a number. Then I would extend that to match (num,num). Finally, I would extend that to match the full pattern. I would not attempt to write the code to match the entire pattern all at once.

Given that the pattern is pretty simple, I would most likely not attempt to replace or move characters.

**~~transgalactic2~~** · 12-27-2008

no
if i see a number i put instead of the first digit 4 or 5 (depends on the location with respect of ',' location to it) and cut off the rest of the digits of the number

4 or 5 are just sign that there is some number here
i compose a BASIC STRUCTURE OF MY INPUT
deleting spaces an changing each number to a single digit
just to say "here is a number"
this function only determines if the input is legal
(1,2) (3,4) (5,6) is a legal input

**laserlight** · 12-27-2008

Originally Posted by transgalactic2

4 or 5 are just sign that there is some number here
i compose a BASIC STRUCTURE OF MY INPUT
deleting spaces an changing each number to a single digit
just to say "here is a number"

Although you could do that, I think that it is unnecessary.

I am going to give you a skeleton of a possible test program:

Code:

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

int is_valid(const char *input);

int main()
{
    char input[] = "(1,2) (34,5) (67,8)";
    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)
{
    /* Fill in your code here (e.g., by using isdigit()) */

    return input;
}

/* Match "(<number>,<number>)" pattern.
 * Return a pointer to the first char after the matched pattern, or
 * NULL if there is no match.
 */
const char *match_pair(const char *input)
{
    if (*input != '(')
    {
        return NULL;
    }

    input = match_number(input + 1);

    /* Fill in your code here */

    return input + 1;
}

/* Match "(<number>,<number>) (<number>,<number>) (<number>,<number>)" pattern.
 * Return 1 if there is a match and 0 otherwise.
 */
int is_valid(const char *input)
{
    input = match_pair(input);
    if (input == NULL)
    {
        return 0;
    }

    /* Fill in your code here */

    return *input == '\0';
}

Notice that instead of your "replace number with a single digit" strategy, I have a function named match_number that simply matches an entire number. I break up the pieces of the pattern into subpatterns that are matched with functions. In this case the pattern is simple enough to just use two such auxiliary functions (and in fact match_number is so simple that I could have integrated it into match_pair without sacrificing readability).

**~~transgalactic2~~** · 12-27-2008

i tried to write the function you said
what is the algorithm for the is_valid function?

Code:

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

int is_valid(const char *input);

int main()
{
    char input[] = "(1,2) (34,5) (67,8)";
    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;
}

/* Match "(<number>,<number>)" pattern.
 * Return a pointer to the first char after the matched pattern, or
 * NULL if there is no match.
 */
const char *match_pair(const char *input)
{
    if (*input != '(')
    {
        return NULL;
    }

    input = match_number(input + 1);

    if (*input=','){
           input = match_number(input + 1);
    }
   if (*input=')'){
           
    }
    else {
     input=NULL;   
    }
    return input + 1;
}

/* Match "(<number>,<number>) (<number>,<number>) (<number>,<number>)" pattern.
 * Return 1 if there is a match and 0 otherwise.
 */
int is_valid(const char *input)
{
    input = match_pair(input);
    if (input == NULL)
    {
        return 0;
    }

    /* Fill in your code here */

    return *input == '\0';
}

**laserlight** · 12-27-2008

Originally Posted by transgalactic2

what is the algorithm for the is_valid function?

Very straightforward: use match_pair() and character comparison with space to check that the input matches the pattern. If at any point match_pair() returns a null pointer or the character in between each pair is not a space, return 0 immediately.

**~~transgalactic2~~** · 12-27-2008

did you mean that?

Code:

const char *match_pair(const char *input)
{
    if (*input != '(')
    {
        return NULL;
    }

    input = match_number(input + 1);

    if (*input=','){
           input = match_number(input + 1);
    }
   if (*input=')'){
           
    }
    else {
     input=NULL;   
    }
    return input + 1;
}

**laserlight** · 12-27-2008

Yes, something like that, though you should be using != instead of = and an empty if block is quite meaningless. You should not be assigning NULL to input since you should return NULL immediately.

**~~transgalactic2~~** · 12-27-2008

i fixed it to..

Code:

const char *match_pair(const char *input)
{
    if (*input != '(')
    {
        return NULL;
    }

    input = match_number(input + 1);

    if (*input==','){
           input = match_number(input + 1);
    }
   if (*input==')'){
           
    }
    else {
     return NULL;   
    }
    return input + 1;
}

**~~transgalactic2~~** · 12-27-2008

did i wrote is_valid correctly??

Code:

int is_valid(const char *input)
{
    input = match_pair(input);
    if (input == NULL)
    {
        return 0;
    }

    else{

    return 1;
    }
    
}

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