foo.cc: In function 'int main()':
foo.cc:10:17: error: expected primary-expression before '%' token
  printf("%d,%d",%a,%b);
                 ^
foo.cc:10:20: error: expected primary-expression before '%' token
  printf("%d,%d",%a,%b);
                    ^
foo.cc:6:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d,%d",&a,&b);
  ~~~~~^~~~~~~~~~~~~~~

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