function index() {
            var height;
            var mass;
            var age;
            height = document.BMI_rechner.height.value;
            mass = document.BMI_rechner.mass.value;
            age = document.getElementById('age').value;
            var bmi = (mass / (height * height)) * 10; //Berechnung
            bmi = Math.round(bmi);
            bmi = bmi / 10;
            document.BMI_rechner.output.value = bmi //Ausgabe

            switch(Number(age)) {
                case (19): document.BMI_rechner.ideal.value = "19 und 24";
                        break;
        }


            if (bmi < 16) {
                document.BMI_rechner.overweight.style.color = "#ffa600";
                document.BMI_rechner.overweight.value = "Sie haben Untergewicht!"
            } else {
                if (bmi > 25) {
                    document.BMI_rechner.overweight.style.color = "#ff0000";
                    document.BMI_rechner.overweight.value = "Sie haben Übergewicht!";
                } else {
                    document.BMI_rechner.overweight.style.color = "#00ff00";
                    document.BMI_rechner.overweight.value = "Sie haben Normalgewicht!";
                }
            }





}