foo.c: In function 'main':
foo.c:7:37: error: expected ';' before '\U0000ff1b'
    7 |         printf("请输入一个正整数：")；
      |                                     ^~
      |                                     ;
foo.c:13:16: error: 'o' undeclared (first use in this function)
   13 |         return o;
      |                ^
foo.c:13:16: note: each undeclared identifier is reported only once for each function it appears in

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