answer.code: In function ‘print_array’:
answer.code:29:9: warning: implicit declaration of function ‘printf’ [-Wimplicit-function-declaration]
         printf("%d ", arr[i]);
         ^~~~~~
answer.code:29:9: warning: incompatible implicit declaration of built-in function ‘printf’
answer.code:29:9: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
answer.code:1:1:
+#include <stdio.h>
 void quick_sort(int arr[], int left, int right) {
answer.code:29:9:
         printf("%d ", arr[i]);
         ^~~~~~
answer.code:31:5: warning: incompatible implicit declaration of built-in function ‘printf’
     printf("\n");
     ^~~~~~
answer.code:31:5: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
answer.code: In function ‘main’:
answer.code:36:5: warning: implicit declaration of function ‘scanf’ [-Wimplicit-function-declaration]
     scanf("%d", &n);
     ^~~~~
answer.code:36:5: warning: incompatible implicit declaration of built-in function ‘scanf’
answer.code:36:5: note: include ‘<stdio.h>’ or provide a declaration of ‘scanf’
answer.code:37:20: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration]
     int* a = (int*)malloc(n * sizeof(int));
                    ^~~~~~
answer.code:37:20: warning: incompatible implicit declaration of built-in function ‘malloc’
answer.code:37:20: note: include ‘<stdlib.h>’ or provide a declaration of ‘malloc’
answer.code:1:1:
+#include <stdlib.h>
 void quick_sort(int arr[], int left, int right) {
answer.code:37:20:
     int* a = (int*)malloc(n * sizeof(int));
                    ^~~~~~
answer.code:54:13: warning: incompatible implicit declaration of built-in function ‘printf’
             printf("-1\n");
             ^~~~~~
answer.code:54:13: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
answer.code:55:13: warning: implicit declaration of function ‘free’ [-Wimplicit-function-declaration]
             free(a);
             ^~~~
answer.code:55:13: warning: incompatible implicit declaration of built-in function ‘free’
answer.code:55:13: note: include ‘<stdlib.h>’ or provide a declaration of ‘free’
answer.code:91:14: warning: implicit declaration of function ‘is_index_in_array’ [-Wimplicit-function-declaration]
         if (!is_index_in_array(ret_, ret_size, i) && !is_index_in_array(ret_, ret_size, j)) {
              ^~~~~~~~~~~~~~~~~
answer.code:101:5: warning: incompatible implicit declaration of built-in function ‘free’
     free(a);
     ^~~~
answer.code:101:5: note: include ‘<stdlib.h>’ or provide a declaration of ‘free’
/usr/bin/ld: /tmp/ccCKjgxE.o: in function `main':
answer.code:(.text.startup+0x23c): undefined reference to `is_index_in_array'
/usr/bin/ld: answer.code:(.text.startup+0x251): undefined reference to `is_index_in_array'
collect2: error: ld returned 1 exit status