Condensed structures are easy to draw and read

Compare the condensed (structural) and expanded (displayed) representations of the hydrocarbons shown below.
 
In the condensed (structural) representation

• carbon-hydrogen bonds are not shown.
  Each carbon is followed directly by the hydrogen atoms bonded to it, the number of hydrogens being shown by the subscript.
  
   
• carbon-carbon single bonds are not shown for carbon chains written on the same line.
  Be careful to draw the bonds from chain to branch carbon atoms from C to C. These are the carbon atoms bonded to each other.
  
   
• carbon-carbon double bonds are always shown using two lines.

Doubly bonded carbons are bonded to fewer hydrogen atoms.