foo.cc: In function 'int rev(int)':
foo.cc:14:17: warning: unused variable 'tmp' [-Wunused-variable]
     int ret(0), tmp(1);
                 ^~~
foo.cc: In function 'int main()':
foo.cc:43:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d",&m,&n);
     ~~~~~^~~~~~~~~~~~~~~

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