else-if

This is not a new construct but we often meet it, as a multi-way decision:

   if (...)
      statement
   else if (...)
      statement
   else if (...)
      statement
   else if (...)
      statement
   else   /* default: none of the above happened */
      statement

C will evaluate the conditions in turn until it reaches the first true one. It then executes its statement and terminates the chain.