foo.cc: In function 'int main()':
foo.cc:4:7: warning: unused variable 'b' [-Wunused-variable]
    4 | int a,b,c,d;
      |       ^
foo.cc:4:9: warning: unused variable 'c' [-Wunused-variable]
    4 | int a,b,c,d;
      |         ^
foo.cc:4:11: warning: unused variable 'd' [-Wunused-variable]
    4 | int a,b,c,d;
      |           ^

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