foo.c: In function 'main':
foo.c:6:19: error: 'A' undeclared (first use in this function)
    6 |     printf("%d",d[A-64]);
      |                   ^
foo.c:6:19: note: each undeclared identifier is reported only once for each function it appears in
foo.c:5:8: warning: variable 'd' set but not used [-Wunused-but-set-variable]
    5 |    int d[2]={0,1};
      |        ^

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