|,|| and &,&& in C#

The && and || operators in C# work very similarly to their And and Or counterparts (& and | in C#).
The difference is that with these operators the second expression is never evaluated
when the first one already determines the outcome of the entire expression
eg: if (userName == “Administrator” && GetNumberOfRecordsFromDatabase() > 0)

Now, GetNumberOfRecordsFromDatabase() will only be executed when the current user is
Administrator. The code will be ignored for all other users, resulting in increased performance for them.

&& in C# is equivalent to AndAlso in C#
|| in C# is equivalent to OrElse in C#

&& and || are not advisable if each and every expression is to be evaluated.

&&' and '||' are what's called "short-circuiting" logical operators.

In the case of &&, if the first operand is false, then it doesn't bother evaluating the second operand, because the whole expression is certain to be false.

In the case of ||, if the first operand is true, then it doesn't bother evaluating the second operand, because the whole expression is certain to be true.

'&' and '|' can also be used as logical operators though it's more common for them to be used as bitwise operators. When they're used as logical operators, both operands are always evaluated.