What is the OR operator in an IF statement

In C#, how do I specify OR:

if(this OR that) {do the other thing}

I couldn't find it in the help.

Update:

My code is:

if (title == "User greeting" || "User name") {do stuff}

and my error is:

Error 1 Operator '||' cannot be applied to operands of type 'bool' and 'string' C:\Documents and Settings\Sky View Barns\My Documents\Visual Studio 2005\Projects\FOL Ministry\FOL Ministry\Downloader.cs 63 21 FOL Ministry

Solution 1:

|| is the conditional OR operator in C#

You probably had a hard time finding it because it's difficult to search for something whose name you don't know. Next time try doing a Google search for "C# Operators" and look at the logical operators.

Here is a list of C# operators.

My code is:

if (title == "User greeting" || "User name") {do stuff};

and my error is:

Error 1 Operator '||' cannot be applied to operands of type 'bool' and 'string' C:\Documents and Settings\Sky View Barns\My Documents\Visual Studio 2005\Projects\FOL Ministry\FOL Ministry\Downloader.cs 63 21 FOL Ministry

You need to do this instead:

if (title == "User greeting" || title == "User name") {do stuff};

The OR operator evaluates the expressions on both sides the same way. In your example, you are operating on the expression title == "User greeting" (a bool) and the expression "User name" (a string). These can't be combined directly without a cast or conversion, which is why you're getting the error.

In addition, it is worth noting that the || operator uses "short-circuit evaluation". This means that if the first expression evaluates to true, the second expression is not evaluated because it doesn't have to be - the end result will always be true. Sometimes you can take advantage of this during optimization.

One last quick note - I often write my conditionals with nested parentheses like this:

if ((title == "User greeting") || (title == "User name")) {do stuff};

This way I can control precedence and don't have to worry about the order of operations. It's probably overkill here, but it's especially useful when the logic gets complicated.

Solution 2:

The OR operator is a double pipe:

||

So it looks like:

if (this || that) 
{
  //do the other thing
}

EDIT: The reason that your updated attempt isn't working is because the logical operators must separate valid C# expressions. Expressions have operands and operators and operators have an order of precedence.

In your case, the == operator is evaluated first. This means your expression is being evaluated as (title == "User greeting") || "User name". The || gets evaluated next. Since || requires each operand to be a boolean expression, it fails, because your operands are strings.

Using two separate boolean expressions will ensure that your || operator will work properly.

title == "User greeting" || title == "User name"

Solution 3:

you need

if (title == "User greeting" || title == "User name") {do stuff};

Solution 4:

Just for completeness, the || and && are the conditional version of the | and & operators.

A reference to the ECMA C# Language specification is here.

From the specification:

3 The operation x || y corresponds to the operation x | y, except that y is evaluated only if x is false.

In the | version both sides are evaluated.

The conditional version short circuits evaluation and so allows for code like:

if (x == null || x.Value == 5)
    // Do something 

Or (no pun intended) using your example:

if (title == "User greeting" || title == "User name") 
    // {do stuff} 

Solution 5:

The conditional or operator is ||:

if (expr1 || expr2) {do stuff}

if (title == "User greeting" || title == "User name") {do stuff}

The conditional (the OR) and it's parts are boolean expressions.

MSDN lists the C# operators in precedence order here http://msdn.microsoft.com/en-us/library/6a71f45d.aspx . And the MSDN page for boolean expressions is http://msdn.microsoft.com/en-us/library/dya2szfk.aspx .

If you are just starting to learn programming, you should read up on Conditional Statements from an introductory text or tutorial. This one seems to cover most of the basics: http://www.functionx.com/csharp/Lesson10.htm .