foo.c: In function 'main':
foo.c:5:9: error: 'if\U0000ff08x1' undeclared (first use in this function)
    5 |         if（x1+x2=y1）;
      |         ^~~~~~
foo.c:5:9: note: each undeclared identifier is reported only once for each function it appears in
foo.c:5:19: error: 'y1\U0000ff09' undeclared (first use in this function)
    5 |         if（x1+x2=y1）;
      |                   ^~~~
foo.c:7:16: error: 'x2\U0000ff01' undeclared (first use in this function)
    7 |         if（x1%x2！=y1）;
      |                ^~~~
foo.c:4:6: warning: unused variable 'x1' [-Wunused-variable]
    4 | {int x1,x2;
      |      ^~

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