/in/foo.c: In function 'main':
/in/foo.c:6:12: warning: format '%f' expects argument of type 'float *', but argument 2 has type 'double *' [-Wformat=]
    6 |    scanf("%f", &a);
      |           ~^   ~~
      |            |   |
      |            |   double *
      |            float *
      |           %lf
/in/foo.c:13:14: error: 'x' undeclared (first use in this function)
   13 |     else if (x >= 500)
      |              ^
/in/foo.c:13:14: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:15:5: warning: this 'else' clause does not guard... [-Wmisleading-indentation]
   15 |     else
      |     ^~~~
/in/foo.c:17:9: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'else'
   17 |         printf("%.2f", b);
      |         ^~~~~~