/in/foo.c: In function 'calculate':
/in/foo.c:9:6: warning: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
    y=sqrt(5*x+10);
      ^~~~
/in/foo.c:9:6: warning: incompatible implicit declaration of built-in function 'sqrt'
/in/foo.c:9:6: note: include '<math.h>' or provide a declaration of 'sqrt'
/in/foo.c:12:14: error: expected expression before 'double'
       return double y;
              ^~~~~~
/in/foo.c:3:10: warning: variable 'y' set but not used [-Wunused-but-set-variable]
   double y;
          ^
/in/foo.c:13:4: warning: control reaches end of non-void function [-Wreturn-type]
    }
    ^