foo.c: In function 'gys':
foo.c:7:6: error: 'xy' undeclared (first use in this function); did you mean 'y'?
    7 |    y=xy
      |      ^~
      |      y
foo.c:7:6: note: each undeclared identifier is reported only once for each function it appears in
foo.c:7:8: error: expected ';' before 'return'
    7 |    y=xy
      |        ^
      |        ;
    8 |  return y;
      |  ~~~~~~ 
foo.c:4:8: warning: variable 'y' set but not used [-Wunused-but-set-variable]
    4 |  int x,y;
      |        ^
foo.c:9:1: warning: control reaches end of non-void function [-Wreturn-type]
    9 | }
      | ^
foo.c: In function 'main':
foo.c:21:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   21 |  scanf("%d%d",&x1,&x2);
      |  ^~~~~~~~~~~~~~~~~~~~~
foo.c:22:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   22 |  scanf("%d%d",&x3,&x4);
      |  ^~~~~~~~~~~~~~~~~~~~~

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