C# Tutorial - Dissecting Our Sixth Application – The Conditional if Statement

The conditional statement ‘if’, selects one of a number of possible statements for execution based on the value of a boolean expression. The ‘if’ statement comes in one of two forms:

if( conditional test ) embedded statement

or

if( conditional test ) 
  true embedded-statement
else
  false embedded-statement

Where:

  • The conditional test evaluates to either true or false and the ‘embedded-statements’ are blocks of code to be executed.

This is best shown in a simple example:

if( i >= 0 )
  Console.WriteLine( "i is a positive number" );
else
  Console.WriteLine( "i is a negative number" );

So what does this mean? Simply put, it means that if the integer in the variable 'i' is greater than or equal to zero, then the application will write the line "i is a positive number" to the console. Otherwise the application will write the line "i is a negative number" to the console. Although the output is not technically correct, it shows how to use an ‘if’ statement. We can fix this allowing us to show nested ‘if’ statements.

if( i >= 0 )
{
  if( i > 0)
    Console.WriteLine( "i is a positive number" );
  else
    Console.WriteLine( "i is zero" );
}
else
  Console.WriteLine( "i is a negative number" );

In the above example, where the embedded-statement is more than a single line, curly braces must be used to denote the scope of the code to be executed.

Shorthand Notation

The conditional statement ‘if .. else’ can be re-written in an alternative form for use in single line statements.

(conditional test) ? true statement : false statement

This is the same as the second version of the ‘if’ statement at the top of the page. This version can be useful for choosing which of two strings to display in a single line.

Comparators

In the second version of the ‘if’ statement, the two 'if' statements have differing boolean comparators. As long as the conditional test evaluates to either a logical true or false, then any of a number of variations may be used. The following table lists the available symbols and there meanings:

Symbol Description
== Is equal to
!= Is not equal to
< Is less than
<= Is less than or equal to
> Is greater than
>= Is greater than or equal to

Boolean Logic

As well as the set of comparators, the conditional test may include boolean logic operators. There are four logical operators that can be used.

Logic Symbol Description
AND && Evaluates to true when the expressions on both sides are true.
OR || Evaluates to true if an expression on either side evaluates to true.
XOR ^ Evaluates to true if one, and only one, expression on either side evaluates to true.
NOT ! Evaluates to true when its expression evaluates to false; otherwise, it returns false (the true/false value of the expression is negated, or reversed).

When used in conjunction with comparators, any logic can be achieved within the conditional test.

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© Publicjoe, 2008