Which one?

//which one is preferable form to use?
//that's the first one

              do //makes sure that scanf puts float into temp
                {
                    printf("How much of artishoks do you want?\n");
                    sc_res= scanf("%f",&temp);
                    if(!sc_res)
                        scanf("%*s");

                }while(!sc_res);

//that's the second one

                printf("How much of artishoks do you want?\n");
                sc_res= scanf("%f",&temp);

                while(!sc_res) //makes sure that scanf puts float into temp
                {
                    scanf("%*s");
                    printf("How much of artishoks do you want?\n");
                    sc_res= scanf("%f",&temp);

                }