title: Check if array index exists
body: <p>Is there any way to check if a given index of an array exists?
  I am trying to set numerical index but something like 1, 5, 6,10. And so I want to see if these indexes already exist and if they do just increase another counter.</p>
  
  <p>I normally work with php but I am trying to do this in c++, so basically I am trying to ask if there is an isset() way to use with c++</p>
  
  <p>PS: Would this be easier with vectors? If so, can anyone point me to a good vector tutorial? Thanks</p>