foo.c:2:5: warning: conflicting types for built-in function 'strlen'; expected 'long unsigned int(const char *)' [-Wbuiltin-declaration-mismatch]
    2 | int strlen(char s[])
      |     ^~~~~~
foo.c:2:1: note: 'strlen' is declared in header '<string.h>'
    1 | #include<stdio.h>
  +++ |+#include <string.h>
    2 | int strlen(char s[])

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