Thread: Creating an array with a piece of a string problem

I am really struggling with this problem! I have included my code although I know there are errors in it. Any help and guidance is greatly appreciated.

Problem as follows:

Write a function named GetSubString that copies a portion of a string. Syntax is as follows: char * GetSubString(const char source[], int start, int count, char result[]);

Where source is the character string containing the substring, start is the position of the first character in source to be copied, count is the number of char to copy and result is an array into which substring is copied. GetSubString returns a pointer to the copied substring but does no printing itself. For example call printf(GetSubString("character", 4, 3, resultArray)); would copy substring "act" from "character" into resultArray, return resultArray, then print "act".

Following are additional requirments:

1. GetSubString must append a '\0' to every substring it creates
2. If start is beyond end of source string, create a substring containing only a '\0'.
3. If count extends beyond end of source, copy characters only up to the end of source string, even though more have been requested
4. No calling of any library functions
5. You may declare only one variable other than forma parameters, if you do it must be a pointer.
6. You must use the following Main, unaltered:

Code:

#include <stdio.h>
#include <stdlib.h>

#define RESULT_MAX 19

int main(void)
{
   static char source[] = "one two three";
   char result[RESULT_MAX];

   puts(GetSubString("This is really fun", 2, 800, result));
   puts(GetSubString("This is really fun", 261, 9, result));
   puts(GetSubString("This is really fun", 0, 12, result));
   puts(GetSubString("source", 5, 87, result));
   puts(GetSubString("source", 18, 7, result));
   puts(GetSubString("source", 6, 5, result));
   puts(GetSubString("source", 0, 3, result));

   return(EXIT_SUCCESS);
}

Here is the beginnings of my code, it doesn't run properly and I know I need to start by figuring out if the start point is before the end of the string ( I have not worked that part out yet)...

Code:

char *GetSubString(const char source[], int start, int count, char result[])
{

  
   {
      for(result[start] = source[start]; start <= (start + count - 1) && start != '\0'; start++)
         result[start] = source[start];
      result[start + 1] = "\0";
   }

   return( *result[0] );
      
}

Thanks for any and all help.

You need to start copying to result[0], not result[start]. Start is your index and should not be compared to '\0'. Perhaps you meant to compare some member of the source array to '\0' instead. start <= (start+count-1) will always be true, unless count is 0. You probably want to assign the character '\0' at the end of the day, not the string "\0".

Still working on same problem, made a couple adjustments so I could take this one bite at a time, I am using whatever variables I need and changed GetSubString into a void function that does printing itself. I've placed a printf function toward the bottom that I hoped would print what is in my result array, but it prints nothing. I am also getting a compiler warning: warning C4047: '=' : 'char' differs in levels of indirection from 'char [2]'

My function call from main is: (GetSubString("character", 4, 3, result));

Thanks for any help past and present...

Code:

void GetSubString(const char *source, int start, int count, char *result)
{
   int i = 0;
   int a = 0;
   
   while ( *source )
   {
      ++source, i++;
   }

   if( start > i)
      result[0] = "\0";
   else
   {
      while (result[a] < result[count] && (*result))
      {
         result[a] = source[start];
         printf("%c", result[a]);                                // debug check
         a++, start++;
      }
     
      
      //for(result[a] = source[start]; a <= count && ( *source ); start++, a++)
        // printf("%c", result[a]);

   }

>> while (result[a] < result[count] && (*result))

You need to compare the indexes, not the characters at those indexes.

OK, I have a working program which meets the assignment criteria....almost.

Here is the original requirements:

Problem as follows:

Write a function named GetSubString that copies a portion of a string. Syntax is as follows: char * GetSubString(const char source[], int start, int count, char result[]);

Where source is the character string containing the substring, start is the position of the first character in source to be copied, count is the number of char to copy and result is an array into which substring is copied. GetSubString returns a pointer to the copied substring but does no printing itself. For example call printf(GetSubString("character", 4, 3, resultArray)); would copy substring "act" from "character" into resultArray, return resultArray, then print "act".

Following are additional requirments:

1. GetSubString must append a '\0' to every substring it creates
2. If start is beyond end of source string, create a substring containing only a '\0'.
3. If count extends beyond end of source, copy characters only up to the end of source string, even though more have been requested
4. No calling of any library functions
5. You may declare only one variable other than formal parameters, if you do it must be a pointer.
6. You must use the following Main, UNALTERED:

I have a couple problems with my code that I can see:

1. By incrementing variable start on in my while loop, the next time the function is called it does not operate properly, namely my if statement evaluates start which was adjusted in the last function call.

2. I am only allowed to use one variable in the whole program, and that must be a pointer. So I need to work out int a and int i out of my code.


Can anyone show me how to remedy these two issues and get this program running properly? Thanks for all your help. This forum is great. Code is as follows:

Code:

#include <stdio.h>
#include <stdlib.h>
#define RESULT_MAX 19

char *GetSubString(const char *source, int start, int count, char *result)
{
   int i = 0;
   int a = 0;
   char *p = source;
 
   
   while ( *p )
   {
      ++p, i++;
   }

   if( start > i)
   {
   result[0] = '\0';
   printf("You lose");              // debug check
   }
   else
   {
      while ( a < count && ( *result ) && a < RESULT_MAX )
      {
         result[a] = source[start];
         a++, start++;
      }
      result[a] = '\0';
   } 

   return(result);
}


int main(void)
{
   static char source[] = "one two three";
   char result[RESULT_MAX];

   //printf(GetSubString("character", 4, 4, result));

   puts(GetSubString("This is really fun", 2, 800, result));
   puts(GetSubString("This is really fun", 261, 9, result));
   puts(GetSubString("This is really fun", 0, 12, result));
   puts(GetSubString("source", 5, 87, result));
   puts(GetSubString("source", 18, 7, result));
   puts(GetSubString("source", 6, 5, result));
   puts(GetSubString("source", 0, 3, result));

   return(EXIT_SUCCESS);
}

It can all be done by simple pointer arithmetic if you take out some time to pen down the algorithm of extracting a substring.

Is there any way you can post the final result?