Execution order of conditions in C# If statement

Question

There are two if statements below that have multiple conditions using logical operators. Logically both are same but the order of check differs. The first one works and the second one fails.

I referred MSDN for checking whether the order of execution of the conditions defined; but I could not find.

Consider a multiple check condition that has && as the logical operator. Is it guaranteed that it will always check the first condition and if that is not satisfied the second condition will not be checked?

I used to use approach 1 and it works well. Looking for an MSDN reference substantiaing the use.

UPDATE

Refer "short-circuit" evaluation

CODE

  List<string> employees = null;      if (employees != null && employees.Count > 0)   {         string theEmployee = employees[0];   }    if (employees.Count > 0 && employees != null)   {         string theEmployee = employees[0];   } 

Answer 1

The && and || operators short-circuit. That is:

1) If && evaluates its first operand as false, it does not evaluate its second operand.

2) If || evaluates its first operand as true, it does not evaluate its second operand.

This lets you do null check && do something with object, as if it is not null the second operand is not evaluated.

Answer 2

You should use:

  if (employees != null && employees.Count > 0)   {         string theEmployee = employees[0];   } 

&& will shortcircuit and employees.Count will not be execucted if employees is null.

In your second example, the application will throw an exception if employees is null when you attempt to Count the elements in the collection.

http://msdn.microsoft.com/en-us/library/2a723cdk(v=vs.71).aspx