I will be having national service serving a military will i get fit and will my stomach will get flat if i enter my national service?

Not necessarily: But you may have a better chance. There will be pros, such as intense physical activities and cons, such as higher levels of stress. Bottom line is you will be able to achieve your goals as long as you are able to control your intake and develop healthy mechanisms to deal with stressful situations. Realistic expectations, when it comes to body changes are critical for success.