foo.cc: In function 'int main()':
foo.cc:7:21: warning: format '%a' expects argument of type 'float*', but argument 2 has type 'int*' [-Wformat=]
  scanf("%a,%b",&a,&b);
                ~~   ^
foo.cc:7:21: warning: unknown conversion type character 'b' in format [-Wformat=]
foo.cc:7:21: warning: too many arguments for format [-Wformat-extra-args]
foo.cc:8:20: warning: unknown conversion type character 'b' in format [-Wformat=]
  printf("%b,%a",b,a);
                    ^
foo.cc:8:20: warning: format '%a' expects argument of type 'double', but argument 2 has type 'int' [-Wformat=]
foo.cc:8:20: warning: too many arguments for format [-Wformat-extra-args]
foo.cc:7:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%a,%b",&a,&b);
  ~~~~~^~~~~~~~~~~~~~~

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