foo.c: In function 'bianli':
foo.c:35:21: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   35 |                 if (f = n - 1)
      |                     ^
foo.c:39:1: warning: control reaches end of non-void function [-Wreturn-type]
   39 | }
      | ^

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