foo.c: In function 'main':
foo.c:28:13: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
             printf("%d\n",i);
             ^~~~~~
foo.c:28:13: warning: incompatible implicit declaration of built-in function 'printf'
foo.c:28:13: note: include '<stdio.h>' or provide a declaration of 'printf'

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