/in/foo.c: In function 'main':
/in/foo.c:7:16: error: redeclaration of 'c' with no linkage
    7 |         double c=(f-32)*5/9;
      |                ^
/in/foo.c:5:14: note: previous declaration of 'c' with type 'double'
    5 |     double f,c;
      |              ^