Is “else if” a single keyword?

Question

I am new to C++. I often see conditional statement like below:

if 
  statement_0;
else if
  statement_1;

Question:

Syntacticall

Answer 1

As already answered, it isn't. They are two keywords. It's start of two statements one following each one other. To try make it a bit more clear, here's the BNF gramar which deal with if and else statements in C++ language.

 statement:      
    labeled-statement
    attribute-specifier-seqopt expression-statement
    attribute-specifier-seqopt compound-statement    
    attribute-specifier-seqopt selection-statement  
    attribute-specifier-seqopt iteration-statement    
    attribute-specifier-seqopt jump-statement  
    declaration-statement
    attribute-specifier-seqopt try-block

   selection-statement: 
         if ( condition ) statement
     if ( condition ) statement else statement

Note that statement itself include selection-statement. So, combinations like:

if (cond1)
   stat
else if(cond2)
   stat
else
   stat

are possible and valid according to C++ standard/semantics.

Note: C++ grammar take from this page.