double mass, height, BMI;
    start:
    cout << "mass? :(kg)"; cin >> mass;
    cout << "height? :(m)"; cin >> height;
    if (height<=0) return 0;
    BMI=mass/pow(height,2);
    cout << "BMI:" << BMI<<endl;
    if(BMI<16) // -------------------------------------------------start of the block
{
    cout << "severly underweight" << endl;
}
    else if (BMI >16 && BMI <=18.5)
     {
         cout<< "underweight"<< endl;
     }
    else if (BMI >18.5 && BMI <=25)
    {
        cout<< "normal" <<endl;
    }
    else if (BMI >25 && BMI <=30)
    {
        cout<< "overweight" << endl;
    }
    else
    {
        cout<<" you are fat" << endl;
    }
    goto start; // loop back
//--------------------------------------------------------end of the block
     return 0;