foo.cc: In function ‘int main()’:
foo.cc:5:15: warning: variable ‘b’ set but not used [-Wunused-but-set-variable]
    5 |         int a,b,c,d;
      |               ^
foo.cc:5:17: warning: variable ‘c’ set but not used [-Wunused-but-set-variable]
    5 |         int a,b,c,d;
      |                 ^
foo.cc:5:19: warning: variable ‘d’ set but not used [-Wunused-but-set-variable]
    5 |         int a,b,c,d;
      |                   ^