permutation.c

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

void swap(char* a, char* b) {
    char t = *a;
    *a = *b;
    *b = t;
}

void perm(char* head, int i, int n) {
    int j;
    if (i+1 == n) {
        puts(head);
    } else {
        for(j=i;j&lt;n;++j) {
            swap(head+i, head+j);
            perm(head, i+1, n);
            swap(head+i, head+j);
        }
    }
}

char buf[] = "abc";

int main(int argc, char* argv[]) {
    perm(buf, 0, strlen(buf));
    return 0;
}