foo.cc: In function 'bign& operator++(bign&, int)':
foo.cc:244:10: warning: reference to local variable 't' returned [-Wreturn-local-addr]
     bign t=a;
          ^
foo.cc: In function 'bign& operator--(bign&, int)':
foo.cc:255:10: warning: reference to local variable 't' returned [-Wreturn-local-addr]
     bign t=a;
          ^
foo.cc: In function 'int main()':
foo.cc:276:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %s",&n,s);
     ~~~~~^~~~~~~~~~~~~~

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