foo.c: In function 'main':
foo.c:6:5: error: unknown type name 'bool'
    6 |     bool flag = 0;
      |     ^~~~
foo.c:2:1: note: 'bool' is defined in header '<stdbool.h>'; did you forget to '#include <stdbool.h>'?
    1 | #include <stdio.h>
  +++ |+#include <stdbool.h>
    2 | 

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