foo.cc: In function 'int main()':
foo.cc:32:21: warning: unused variable 'p' [-Wunused-variable]
   32 |                 int p=i;
      |                     ^
foo.cc:28:14: warning: unused variable 'flag' [-Wunused-variable]
   28 |         bool flag=false;
      |              ^~~~
foo.cc: In function 'int yunsuan(int, int, char)':
foo.cc:9:1: warning: control reaches end of non-void function [-Wreturn-type]
    9 | }
      | ^

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