foo.c: In function 'main':
foo.c:4:6: warning: 'main' is normally a non-static function [-Wmain]
    4 | {int main()
      |      ^~~~
foo.c: In function 'main':
foo.c:7:1: error: 'cin' undeclared (first use in this function)
    7 | cin>>n1;
      | ^~~
foo.c:7:1: note: each undeclared identifier is reported only once for each function it appears in
At top level:
foo.c:4:6: warning: 'main' defined but not used [-Wunused-function]
    4 | {int main()
      |      ^~~~

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