recursive string operation..

**~~transgalactic2~~** · 01-08-2009

Originally Posted by itCbitC

redo the code with proper indentation; index is a local variable and everytime merge_strings() is invoked index is reset to zero due to this int res,index=0; in merge_strings().

i was told here that index=0 is a problem
so i removed it

do i need to put index=0
??

**~~transgalactic2~~** · 01-08-2009

Originally Posted by transgalactic2

i was told here that index=0 is a problem
so i removed it

do i need to put index=0
??

i didnt understand him correctly.
i will change the code

**~~transgalactic2~~** · 01-08-2009

i changed it
like itCbitC said.
i dont get the exe error but i dont have any output either

??

Code:

#include <stdio.h>
int merge_strings(char str1[], int index1,char str2[],int index2, char result[], int index3);
int main() {
    char input[255];
    char input2[255];
    char result[510];
    int index,flag,ch;
    printf("enter the first string \n");
 for (index = 0; index < 254 && (ch = getchar()) != '\n' && ch >=0; ++index)
    {
        input[index] = ch;
    }

    input[index] = '\0';

    printf("enter the second string \n");
 for (index = 0; index < 254 && (ch = getchar()) != '\n' && ch >=0; ++index)
    {
        input2[index] = ch;
    }

    input2[index] = '\0';
    flag=merge_strings(input, 0,input2,0, result, 0);

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

return 0;
}


int merge_strings(char str1[], int index1,char str2[],int index2, char result[], int index3)
 {
      int res,index=0;
      int res2;
      //start checking apha chars for string 1
     if ((((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))&&(index==254))
     {

         return 1;
     }
     if (((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))
     {

         res=merge_strings(str1, index1++,str2,index2, result, index3);
     }
     else
     {
       return 0;
     }
     //end checking apha chars for string 1

      //start checking apha chars for string 2
    if ((((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))&&(index==254))
       {

         return 1;
     }
     if (((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))
     {

         res2=merge_strings(str1, index1,str2,index2++, result, index3);
     }
     else
     {
       return 0;
     }
     //end checking apha chars for string 2

     if ((res==1)&&(res2==1))
     {
         result[index3]=str1[index];
         if(index1<255)
         {
             res=merge_strings(str1, index1++,str2,index2, result, index3++);
         }

         result[index3]=str2[index2];
         if(index2<255)
         {
             res=merge_strings(str1, index1,str2,index2++, result, index3++);
         }

     }
     return 1;
}

**matsp** · 01-08-2009

So, now the question is: Where does index change? And what do you actually use index for in your function?

--
Mats

**~~transgalactic2~~** · 01-08-2009

i removed index. and i changed the code to the proper "index" from the signature

it doesnt give me an output at all

??

Code:

#include <stdio.h>
int merge_strings(char str1[], int index1,char str2[],int index2, char result[], int index3);
int main() {
    char input[255];
    char input2[255];
    char result[510];
    int index,flag,ch;
    printf("enter the first string \n");
 for (index = 0; index < 254 && (ch = getchar()) != '\n' && ch >=0; ++index)
    {
        input[index] = ch;
    }

    input[index] = '\0';

    printf("enter the second string \n");
 for (index = 0; index < 254 && (ch = getchar()) != '\n' && ch >=0; ++index)
    {
        input2[index] = ch;
    }

    input2[index] = '\0';
    flag=merge_strings(input, 0,input2,0, result, 0);

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

return 0;
}


int merge_strings(char str1[], int index1,char str2[],int index2, char result[], int index3)
 {
      int res;
      int res2;
      //start checking apha chars for string 1
     if ((((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))&&(index1==254))
     {

         return 1;
     }
     if (((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))
     {

         res=merge_strings(str1, index1++,str2,index2, result, index3);
     }
     else
     {
       return 0;
     }
     //end checking apha chars for string 1

      //start checking apha chars for string 2
    if ((((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))&&(index1==254))
       {

         return 1;
     }
     if (((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))
     {

         res2=merge_strings(str1, index1,str2,index2++, result, index3);
     }
     else
     {
       return 0;
     }
     //end checking apha chars for string 2

     if ((res==1)&&(res2==1))
     {
         result[index3]=str1[index1];
         if(index1<255)
         {
             res=merge_strings(str1, index1++,str2,index2, result, index3++);
         }

         result[index3]=str2[index2];
         if(index2<255)
         {
             res=merge_strings(str1, index1,str2,index2++, result, index3++);
         }

     }
     return 1;
}

**matsp** · 01-08-2009

So, AGAIN: What is your exit condition. What do you have to do to get there?

--
Mats

**~~transgalactic2~~** · 01-08-2009

this is my exit condition

Code:

if ((((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))&&(index1==254))
     {

         return 1;
     }

it returns 1 when all the chars are ok.

in the merging part when the index reaches 255 it doesnt go to the if again
thus stopping the recursion and returning 1

**anon** · 01-08-2009

Doesn't merging mean that you pick characters from one or another string so that the resulting string would also be in ascending order? Otherwise what is the purpose of checking whether the input strings are in ascending order?

Or is this task simply a collection of pretty arbitrary requirements (I don't see any relevance in the A...Z check) in hope that no other teacher has ever asked anybody to write such a bizarre program (and you can't search for the code on the internet)?

this is my exit condition

This exit condition would appear to be always false (the last character in the max-length string shouldn't be anything other than '\0'), or you have already passed the end of the string and the result of that is undefined...

Also, could you for a start write this using a simple loop. It is usually trivial to turn a single loop into a recursion.

**matsp** · 01-08-2009

Originally Posted by transgalactic2

this is my exit condition

Code:

if ((((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))&&(index1==254))
     {

         return 1;
     }

it returns 1 when all the chars are ok.

in the merging part when the index reaches 255 it doesnt go to the if again
thus stopping the recursion and returning 1

And how long is the string you have entered?

--
mats

**~~transgalactic2~~** · 01-08-2009

Originally Posted by anon

Doesn't merging mean that you pick characters from one or another string so that the resulting string would also be in ascending order? Otherwise what is the purpose of checking whether the input strings are in ascending order?

Or is this task simply a collection of pretty arbitrary requirements (I don't see any relevance in the A...Z check) in hope that no other teacher has ever asked anybody to write such a bizarre program (and you can't search for the code on the internet)?

This exit condition would appear to be always false (the last character in the max-length string shouldn't be anything other than '\0'), or you have already passed the end of the string and the result of that is undefined...

i do need to pick up from the last place of the first string
thats why i put index3++ on both calls

**~~transgalactic2~~** · 01-08-2009

ok i understand that str2 is written over str1 places

i dont know how to fix it

**itCbitC** · 01-08-2009

Originally Posted by transgalactic2

i removed index. and i changed the code to the proper "index" from the signature

it doesnt give me an output at all

??

Code:

//start checking apha chars for string 2
    if ((((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))&&(index1==254))

what do you think should go here? str1 or str2?
maybe that's why you are not getting any output at all.
post the entire code again, one more time (hopefully better indented).

**anon** · 01-08-2009

So you want to copy first string and append the other? Can you do this with a loop? The other things like testing for order and character values is just a distraction that has little to do with the recursion (except perhaps you have to reserve the return value for signalling error).

Also, does it have to be all just one function, besides main?

Otherwise it might go something like this:

Code:

int recursive_copy_with_weird_extra_conditions(char** result, const char* input);

int funny_merge(const char* first, const char* second, char* result)
{
    return recursive_copy_with_weird_extra_conditions(&result, first) ||recursive_copy_with_weird_extra_conditions(&result, second);
}

**matsp** · 01-08-2009

Originally Posted by anon

Also, does it have to be all just one function, besides main?

I asked that very same question.

I wrote a pretty simple piece of code that does the required work here - it's about 70 lines including main. But it uses 4 functions (which could be reduced a bit, since I have one function simply to check if it's a letter in the right range). It does ALL of the work using recursion (except for reading the string, where I cheated and used fgets()).

And to paraphrase Salem, this is like tying your shows using only your left hand - it's nothing useful to learn [unless someone has chopped off your right hand of course].

--
Mats

**~~transgalactic2~~** · 01-08-2009

i did itCbitC change
its not giving me an output

Code:

#include <stdio.h>
int merge_strings(char str1[], int index1,char str2[],int index2, char result[], int index3);
int main() {
    char input[255];
    char input2[255];
    char result[510];
    int index,flag,ch;
    printf("enter the first string \n");
 for (index = 0; index < 254 && (ch = getchar()) != '\n' && ch >=0; ++index)
    {
        input[index] = ch;
    }

    input[index] = '\0';

    printf("enter the second string \n");
 for (index = 0; index < 254 && (ch = getchar()) != '\n' && ch >=0; ++index)
    {
        input2[index] = ch;
    }

    input2[index] = '\0';
    flag=merge_strings(input, 0,input2,0, result, 0);

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

return 0;
}


int merge_strings(char str1[], int index1,char str2[],int index2, char result[], int index3)
 {
      int res;
      int res2;
      //start checking apha chars for string 1
     if ((((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))&&(index1==254))
     {
          return 1;
     }
     if (((str1[index1]>= 65) &&(str1[index1]<= 90))||((str1[index1]>= 97) &&(str1[index1]<= 122)))
     {
          res=merge_strings(str1, index1++,str2,index2, result, index3);
     }
     else
     {
         return 0;
     }
     //end checking apha chars for string 1

      //start checking apha chars for string 2
    if ((((str2[index2]>= 65) &&(str2[index2]<= 90))||((str2[index2]>= 97) &&(str2[index2]<= 122)))&&(index2==254))
     {

         return 1;
     }
     if (((str2[index2]>= 65) &&(str2[index2]<= 90))||((str2[index2]>= 97) &&(str2[index2]<= 122)))
     {

         res2=merge_strings(str1, index1,str2,index2++, result, index3);
     }
     else
     {
         return 0;
     }
     //end checking apha chars for string 2

     if ((res==1)&&(res2==1))
     {
         result[index3]=str1[index1];
         if(index1<255)
         {
             res=merge_strings(str1, index1++,str2,index2, result, index3++);
         }

         result[index3]=str2[index2];
         if(index2<255)
         {
             res=merge_strings(str1, index1,str2,index2++, result, index3++);
         }

     }
     return 1;
}

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