Thread: String permutation not working

I have bee trying to work this out for a couple of hours now, I am getting nowhere and its annoying.

Here is some working code to display string permutations in C++:

Code:

#include <iostream>
#include <string>
using namespace std;

string swtch(string topermute, int x, int y)
{
    string newstring = topermute;
	newstring[x] = newstring[y];
	newstring[y] = topermute[x]; //avoids temp variable
	return newstring;
}

void permute(string topermute, int place)
{
	if(place == topermute.length() - 1)
	{
    	cout<<topermute<<endl;
    }
    for(int nextchar = place; nextchar < topermute.length(); nextchar++)
	{
		permute(swtch(topermute, place, nextchar), place+1);
	}
}

int main()
{
    permute("love", 0);
	system("PAUSE");
}

I tried to convert this to C. Here is what I got:

Code:

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

char *CharSwap(char *word, int x, int y)
{
    char temp = word[x];
    word[x] = word[y];
    word[y] = temp;
	return word;
}

void Permute(char *word, int pos)
{
	int len=strlen(word);
	int next;
	
    if(pos == len-1)
		printf("%s\n", word);
		
	for(next=pos; next<len; next++)
		Permute(CharSwap(word, pos, next), pos+1);
}

int main()
{
    char word[]="love";
    Permute(word, 0);
    system("PAUSE");
}

If someone could please explain why the second version in C does not work correctly it would be much appreciated by me. Thanks.

Thanks for pointing that out @nthony, It seems obvious now I know. Anyway I got a working version now. Its a lot more code, but at least it works. Cheers.

Code:

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

struct perm
{
    char mutate[20];
};
typedef struct perm perm; 

void Permute(char *word, int pos, perm *p)
{
	int len=strlen(word);
	int next;
    char temp; 
       
    //First time run: Allocate space, and copy word to first address
    if(pos == 0)
    {
        int permutations=1;   
        for(next=2; next<=len; next++)
            permutations*=next;
        p = malloc(permutations*10);// *10 to be safe for duplicates
        strcpy(p->mutate, word);
    }
    //Use 'word' as temp. Move to next address. Put copy to new address
    else
    {
        strcpy(word, p->mutate); 
        p++;                     
        strcpy(p->mutate, word); 
    }
        
    if(pos == len-1)
		printf("%s\n", p->mutate);
		
	for(next=pos; next<len; next++)
    {
        temp = p->mutate[pos];
        p->mutate[pos] = p->mutate[next];
        p->mutate[next] = temp;    
        Permute(word, pos+1, p);      	
    }
    
    //When all recursions complete free allocated memory
    if(pos==0)free(p); 
}

int main()
{
    char word[10]; 
    int len;
    printf("Enter a word up to 8 characters in length: ");
    fgets(word, 10, stdin); len=strlen(word)-1; word[len]='\0'; 
    Permute(word, 0, NULL);
    system("PAUSE");
}