/in/foo.c: In function 'main':
/in/foo.c:7:14: error: 'F' undeclared (first use in this function)
  scanf("%d",&F);
              ^
/in/foo.c:7:14: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:9:14: warning: format '%d' expects argument of type 'int', but argument 2 has type 'double' [-Wformat=]
  printf("C= %d\n",c);
              ^