C - recursive permutations in lexicographical order - c

Question

I am trying to make permutations of strings with up to 8 characters. The problem is it must be done with recursion and it must be in lexicographical order. I found one solution with the recursion but it only works for 4 characters max. After that, it starts to mess up again.
void swap(char* a, char* b){
char temp = *a;
*a = *b;
*b = temp;
}
void recursion(char* arr, int start, int n){
if (start == (n-1)){
printf("%s\n", arr);
return;
}
for (int i = start; i < n; i++){
recursion(arr, start+1, n);
swap(arr+start+1, arr+n-1);
int j = start+1;
while (j < n && arr[start] > arr[j]){
j++;
}
if (j >= n){
continue;
}
swap(arr+start, arr+j);
}
swap(arr+start+1, arr+n-1);
}
int main(int argc, char *argv[]) {
char arr[9];
char charakter;
int m = 0;
while (scanf("%c", &charakter) != EOF){
if (charakter == '\n'){
break;
}
else if (isalpha(charakter) || isdigit(charakter)){
arr[m] = charakter;
m++;
}
else{
fprintf(stderr, "Error!\n");
return 100;
}
}
arr[m] = '\0';
int n = strlen(arr);
int start = 0;
recursion(arr, start, n);
return 0;
}
Any idea how to fix the recursion function?

Answer 1

Your solution is strange, have a look here and here a fix:
void recursion(char *arr, int start, int n) {
if (start == n) {
printf("%s\n", arr);
return;
}
for (int i = start; i < n; i++) {
swap(arr + start, arr + i);
recursion(arr, start + 1, n);
swap(arr + start, arr + i);
}
}
here a proper solution:
#include <ctype.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
static void recursion(char *str, size_t n, size_t max) {
if (n < max) {
recursion(str, n + 1, max);
for (size_t i = n + 1; i < max; i++) {
char tmp = str[i];
str[i] = str[n];
str[n] = tmp;
recursion(str, n + 1, max);
str[n] = str[i];
str[i] = tmp;
}
} else {
printf("%s\n", str);
}
}
int main(void) {
char str[42];
errno = 0;
if (scanf("%41s", str) != 1) {
if (errno != 0) {
perror("scanf()");
} else {
fprintf(stderr, "no input");
}
return 1;
}
recursion(str, 0, strlen(str));
}