Can I quit alcohol and cigarettes at the same time?

I have been a smoker for about 8 years and smoke about a pack per day. I am also an alcoholic and now drink about 7 to 10 beers a day, and have been for the past 2.5 years. Last night I decided to quit drinking beer every day and today I am already shaky, nervous, and can't concentrate. I want to quit smoking also so I can join the army. Is it dangerous to quit both at once? Would it be too much stress on my body and mind? And also, would having just one beer a day for the next couple days help with the withdrawal symptoms?