Question

I am trying to print all possible combinations of the string ‘abc’ using C. Can someone help point out where in this code I am going wrong ? I am using the algorithm mentioned here:
http://hackercs.com/videos/Combinations-of-a-String-Part-2/
Thanks for your time and help. ( BTW, the goal is to use recursion here)

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


 void combination(char **curString,int allowedStart,char **outBuffer,int length)
{
//check for allowed chars.
// if not return.
// else
// for each char in the allowed char
// copy into buffer
//print buffer
//combine buffer and over next allowed chars
//remove from buffer.

if (allowedStart == length)
    return;
else    
   {
int curr;
for (curr = allowedStart;curr<length; curr++){
//need to copy 'a' into outbuffer and keep appending to outbuffer.
printf("allowedStart = %d\n",allowedStart);
printf("curr = %d\n",curr);

(*outBuffer)[curr] = (*curString)[allowedStart];
printf("outbuff is %s\n",*outBuffer);       

combination(curString,curr+1,outBuffer,length);
    printf("return\n");
(*outBuffer)[length-1] = '\0';

   } //else
} //for 
}

 main()
 {
 char *var = "abc";
 int length = strlen(var);
 printf("length = %d\n",length);

 char *outBuffer = malloc ( length * sizeof (char));
 bzero(outBuffer,3);
 combination(&var,0,&outBuffer,length);

  }

Answer 1

Got this working.

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


void combination(char **curString,int allowedStart,char **outBuffer,int length)
{
    //check for allowed chars.
    // if not return.
    // else
    // for each char in the allowed char
    // copy into buffer
    //print buffer
    //combine buffer and over next allowed chars
    //remove from buffer.
    int curr;

    if ( allowedStart == length )
        return;
    else    {

            for (curr = allowedStart;curr<length; curr++){
        //need to copy 'a' into outbuffer and keep appending to outbuffer.
        //      printf("allowedStart= %d  curr= %d \n",allowedStart,curr);

                (*outBuffer)[curr] = (*curString)[allowedStart];
                //adjust for appending.

                int i = 0;
                while (i < length)
                {
                    if ( ((*outBuffer)[i] == '\0') && ((*outBuffer)[i+1] != '\0') )
                    {
        //              printf("in here\n");
                        (*outBuffer)[i] = (*outBuffer)[i+1];
                        (*outBuffer)[i+1] = '\0';
                    }
                    i++;
                }

        //      printf("added curr%d %c \n",curr, (*outBuffer)[curr]);
                printf("***************************************COMBO: %s\n",*outBuffer);        
                allowedStart = curr+1;
        //      printf("allowedStart%d %c \n",allowedStart,(*curString)[allowedStart]);

                combination(curString,allowedStart,outBuffer,length);
        //      printf("removing%d %c\n",curr,(*outBuffer)[curr]);
                (*outBuffer)[curr] = ' ';   
        //      printf("**************RETURNCOMBO: %s\n",*outBuffer);       

        } //else
    } //for 
}

main()
{
    char *var = "abcd";
    int length = strlen(var);
    printf("length = %d\n",length);
//  printf("Intial word is %s\n",var);
    char *outBuffer = malloc ( (length+1) * sizeof (char));
    bzero(outBuffer,length);
    combination(&var,0,&outBuffer,length);

}