/in/foo.c: In function 'main':
/in/foo.c:24:16: warning: implicit declaration of function 'malloc' [-Wimplicit-function-declaration]
     int* arr = malloc(n * sizeof(int));
                ^~~~~~
/in/foo.c:24:16: warning: incompatible implicit declaration of built-in function 'malloc'
/in/foo.c:24:16: note: include '<stdlib.h>' or provide a declaration of 'malloc'
/in/foo.c:30:5: warning: implicit declaration of function 'free' [-Wimplicit-function-declaration]
     free(arr);
     ^~~~
/in/foo.c:30:5: warning: incompatible implicit declaration of built-in function 'free'
/in/foo.c:30:5: note: include '<stdlib.h>' or provide a declaration of 'free'