Thread: recursive string operation..

I need to build a function which gets two strings checks if their chars are alpha type
in ascending order.
If they both are then it needs to merge them in a third d string.

I cant call external functions.

The whole process must be in one function
and no iterative loops
and only in a recursive way.

I tried to build this function.

i think it works
but just after i input
abc in the first string and def into the second one

it does nothing and says that my program the EXE file
encountered a problem
and needs to be closed

why??

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;
      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, index++,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, index,str2,index2++, result, index3);
     }
     else
     {
       return 0;
     }
     //end checking apha chars for string 2

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

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

     }
     return 1;
}

IMO, revisit the algorithm you have tried to to code because there are a few things you seem to have left out from the program implementation.
Also it's way better to compare chars instead of their value as in str1[index1]>= 'A' is the preferred way instead of str1[index1]>= 65. Just my 2c.

Run-Time Check Failure #3 - The variable 'index' is being used without being initialized.
Listen to your compiler warnings!

Code:

     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, index++,str2,index2, result, index3);
     }
     else
     {
       return 0;
     }

Could we not do this a bit simpler, since there is two exactly identical checks here...

--
Mats

Originally Posted by transgalactic2

what things i leftout?

For starters you need to loop through the string comparing each element with the next one and making sure that they are in alphabetically ascending order.
ATM you are not doing, that is, not comparing adjacent elements to make sure that each element is an alphabet and is lexically less than its successor.

Originally Posted by transgalactic2

i have zero warnings.

Then turn up the warnings! Uninitialized variables are quite serious.

index3 does not need to be initialized because it comes from the signature of the function.

Not talking about index3. Talking about index.

Originally Posted by transgalactic2

The first "if" is the stop case were it reaches the end of the string.
The second "if" is for keep checking if the chars till now are correct and it checks the
next one.

i cant think of doing it in another way.

where is the problem in the algorithm?

The problem is that it's too complicated. So check the common thing first, then use a separate if-statement inside that to avoid rechecking four rather complicated conditions.

Also, you can't call any external function, but as I read it, you should be able to call YOUR OWN LOCAL functions. So perhaps you can write one that checks if a char is a letter A-Z, a-z. And please use character constants rather than 65, 90, 97, 122, etc. It makes it MUCH easier to read if some constant is 'A' than 65.

--
Mats