foo.c: In function 'main':
foo.c:4:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    4 |  scanf("%d", &n);
      |  ^~~~~
foo.c:4:2: warning: incompatible implicit declaration of built-in function 'scanf'
foo.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | int main()
foo.c:13:5: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   13 |     printf("%d %d\n", i, j);
      |     ^~~~~~
foo.c:13:5: warning: incompatible implicit declaration of built-in function 'printf'
foo.c:13:5: note: include '<stdio.h>' or provide a declaration of 'printf'

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