Equality and Relational Operators

• = = != //be careful with = =
• < > <= >=
• Boolean expressions: not, and, or ! && ||
• Precedence revisited

• Not sequential
• When needed to choose between two (or more) alternatives
• IF syntax for single statements

if ( condition )
   statement;
• examples of Javascript code

if ( input_num < 0 )
      document.write ( "Error message<br>");
• IF syntax for multiple statements

if ( condition )
{
           statement₁;
           statement₂;
}
• examples of Javascript code

if ( grade == 100 )
{
          document.write( "Excellent job<br>");
          bonus = 1;
}

IF-ELSE syntax

• single statements

if ( condition )
     statement;
else
     statement;
• examples of Javascript code

if (x < 0 )
     document.write( "negative number<br>");
else
     document.write( "non-negative number<br>");
• Nested IFs
  • More than two possible actions
  • Second if can be nested inside of the 1^st "if" part or the 1^st "else" part
  • Examples
  
  if ( x <0 )
       document.write( "negative number<br>");
  else
       if ( x == 0 )
       document.write( "zero<br>");
  else
            document.write( "positive number<br>");
   

if (x < 0 )
     document.write( "negative number<br>");
else if (x == 0)
     document.write( "zero<br>");
else
     document.write(" "positive number<br>");

• Used in place of if-elseif-elseif…
• Syntax

switch ( variable)
{
     case1:     statements;
          break;
     case2:     statements;
          break;
     . . .
     casen:     statements;
          break;
     default:     statements;
}