/in/foo.cc:3:11: error: 'double y1' redeclared as different kind of entity
    3 | double x1,y1,x2,y2,sum;
      |           ^~
In file included from /usr/include/features.h:489,
                 from /usr/include/x86_64-linux-gnu/c++/12/bits/os_defines.h:39,
                 from /usr/include/x86_64-linux-gnu/c++/12/bits/c++config.h:655,
                 from /usr/include/c++/12/cassert:43,
                 from /usr/include/x86_64-linux-gnu/c++/12/bits/stdc++.h:33,
                 from /in/foo.cc:1:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:224:1: note: previous declaration 'double y1(double)'
  224 | __MATHCALL (y1,, (_Mdouble_));
      | ^~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:6:17: warning: format '%lf' expects argument of type 'double*', but argument 3 has type 'double (*)(double) noexcept' {aka 'double (*)(double)'} [-Wformat=]
    6 |     scanf("%lf%lf%lf%lf", &x1,&y1,&x2,&y2);
      |               ~~^             ~~~
      |                 |             |
      |                 double*       double (*)(double) noexcept {aka double (*)(double)}
/in/foo.cc:7:40: error: invalid operands of types 'double(double) noexcept' {aka 'double(double)'} and 'double' to binary 'operator-'
    7 |         sum = sqrt( (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2) );
      |                                      ~~^~~
      |                                      |  |
      |                                      |  double
      |                                      double(double) noexcept {aka double(double)}
/in/foo.cc:7:48: error: invalid operands of types 'double(double) noexcept' {aka 'double(double)'} and 'double' to binary 'operator-'
    7 |         sum = sqrt( (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2) );
      |                                              ~~^~~
      |                                              |  |
      |                                              |  double
      |                                              double(double) noexcept {aka double(double)}