foo.c: In function 'main':
foo.c:8:19: error: 'xi' undeclared (first use in this function); did you mean 'x'?
    8 |     for(int x=2;x<xi;x++)
      |                   ^~
      |                   x
foo.c:8:19: note: each undeclared identifier is reported only once for each function it appears in
foo.c:4:7: warning: unused variable 'x' [-Wunused-variable]
    4 | { int x,x1;
      |       ^

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