/in/foo.c:2:6: warning: return type of 'main' is not 'int' [-Wmain]
 void main()
      ^~~~
/in/foo.c: In function 'main':
/in/foo.c:4:16: error: expected ')' before '<=' token
     float c,f(o<=f<=1000);
                ^~
/in/foo.c:5:14: error: 'f' undeclared (first use in this function)
  scanf("%f",&f);
              ^
/in/foo.c:5:14: note: each undeclared identifier is reported only once for each function it appears in