foo.c: In function ‘main’:
foo.c:20:22: error: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration]
   20 |     int* arr = (int*)malloc(sizeof(int) * n);
      |                      ^~~~~~
foo.c:2:1: note: include ‘<stdlib.h>’ or provide a declaration of ‘malloc’
    1 | #include<stdio.h>
  +++ |+#include <stdlib.h>
    2 | void sort(int arr[], int n){
foo.c:20:22: warning: incompatible implicit declaration of built-in function ‘malloc’ [-Wbuiltin-declaration-mismatch]
   20 |     int* arr = (int*)malloc(sizeof(int) * n);
      |                      ^~~~~~
foo.c:20:22: note: include ‘<stdlib.h>’ or provide a declaration of ‘malloc’