c - Combinations of elements in an array -

i'm trying write c program find combinations of given array , specified length. i've done far..

#include <stdio.h>  void com(int* a, int* t, int len, int i) {      int j, k;      if(len == 0) {          for(k=0;k<3;k++) {             printf("%d  ",t[k]);         }          printf("\n");         return;     }      for(j = ; j <= 4-len ; j++) {  // 4 = original array size          t[3-len] = a[j];         com(a,t,len-1,i+1);     } }  main() {      int t[3];     com((int[]){4,1,3,2},&t[0],3,0); // 3 = combination length } 

the problem in code has no option skip duplicates, repetitions of combination. e.g array {1,2,3,4} generates

1  2  3   1  2  4   1  3  3   1  3  4   2  2  3   2  2  4   2  3  3   2  3  4  

but supposed generate

1 2 3 1 2 4 1 3 4 2 3 4 

what can that? i'm not sure how that. kind of appreciated. thanks.

also, if there alternative , better optimized solution this, feel free share.

sample fix

void com(int *a, int *t, int len, int i){     if(i == len){         for(int k = 0; k < len; k++)             printf("%d ", t[k]);         printf("\n");         return;     }     while(*a){         t[i] = *a;         com(++a, t, len, i+1);     } }  int main(void){     int t[3];      com((int[]){1,2,3,4, 0}, t, 3, 0);     //                   ^end mark     return 0; }