foo.cc: In function 'int main()':
foo.cc:8:16: error: 'x1' was not declared in this scope
    8 | scanf("%d %d",&x1,&x2);
      |                ^~
foo.cc:8:20: error: 'x2' was not declared in this scope
    8 | scanf("%d %d",&x1,&x2);
      |                    ^~
foo.cc:5:5: warning: unused variable 'a' [-Wunused-variable]
    5 | int a;
      |     ^
foo.cc:6:5: warning: unused variable 'b' [-Wunused-variable]
    6 | int b;
      |     ^

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