title: Can I define variable in Julia just like in Fortran
body: <p>I am new to Julia. Have a quick question.
  In Fortran, we can do</p>
  <pre><code>implicit none
  </code></pre>
  <p>Therefore whenever we use a variable, we need to define it first. Otherwise it will give error.</p>
  <p>In Julia, I want to do the same time thing. I want to define the type of each variable first, like Float64, Int64, etc. So that I wish that Julia no longer need to automatically do type conversion, which may slow down the code.
  Because I know if Julia code looks like Fortran it usually runs fast.</p>
  <p>So, in short, is there a way in Julia such that, I can force it to only use variables whose types has been defined, and otherwise give me an error message? I just want to be strict.</p>
  <p>I just wanted to define all the variables first, then use them. Just like Fortran does.</p>
  <p>Thanks!</p>
  <p>[Edit]</p>
  <p>As suggested by the experts who answers the questions, thank you very much! I know that perhaps in Julia there is no need to manually define each variables one by one. Because for one thing, if I do that, the code will become just like Fortran, and it can be very very long especially if I have many variables.</p>
  <p>But if I do not define the type of the each variables, is Julia smart enough to know the type? Will it do some conversions which may slow down the code?</p>
  <p>Also, even if there is no need to define variables one by one, is there in some situations we may have to manually define the type manually?</p>