C# .NET

Conditional Logicin C# .Net

 

 

Conditional Logic is all about the IF word. In fact, it’s practically impossible
to programme effectively without using IF. You can write simple programmes
like our calculator. But for anything more complicated, you need to get the
hang of Conditional Logic.

As an example, take the calculator programme you have just written. It only
has a Plus button. We’ll be adding another button soon, a Subtract button.
Now, you can’t say beforehand which of the two buttons your users will click.
Do they want to add, or subtract? You need to be able to write code that does
the following:

IF the Plus button was clicked, add up
IF the Minus button was clicked, subtract

You can rearrange the two statements above.

Was the Plus button clicked? Yes, or No?
Was the Minus button clicked? Yes, or No?

So the answer for each is either going to be Yes, or No – the button is either
clicked, or not clicked.

 

C# IF Statements

To test for YES or NO values, you can use an IF statement. You set them up
like this:

if ( )
{

}

So you start with the word if (in lowercase), and type a pair of round
brackets. In between the round brackets, your type what you want to check
for (Was the button clicked?). After the round brackets, it’s convenient (but
not strictly necessary) to add a pair of curly brackets. In between your curly
brackets, you type your code. Your code is what you want to happen IF the
answer to your question was YES, or IF the answer was NO. Here’s a coding
example:

bool buttonClicked = true;

if (buttonClicked = = true)
{

MessageBox.Show(“The button was clicked”);

}

Notice the first line of code:

bool buttonClicked = true;

This is a variable type you haven’t met before – bool. The bool is short
for Boolean. You use a Boolean variable type when you want to check
for true or false values (YES, or NO, if you prefer). This type of variable
can only ever be true or false. The name of the bool variable above is buttonClicked.
We’ve set the value to true.

The next few lines are our IF Statement:

if (buttonClicked == true)
{

MessageBox.Show(“The button was clicked”);

}

The double equals sign ( ==) is something else you need to get used to when
using IF Statements. It means “Has a value of”. The double equals
sign is known as a Conditional Operator. (There are a few others that
you’ll meet shortly.) But the whole of the line reads:

“IF buttonClicked has a value of true”

If you miss out one of the equals signs, you’d have this:

if (buttonClicked = true)

What you’re doing here is assigning a value of true to the variable buttonClicked.
It’s not checking if buttonClicked “Has a value of” true. The difference
is important, and will cause you lots of problems if you get it wrong!

In between the curly brackets of the IF statement, we have a simple MessageBox
line. But this line will only get executed IF buttonClicked has a value of
true.

Let’s try it out. Start a new project for this (File > New Project). Add
a button to your new form, and set the Text property to “IF Statement”.
Double click the button, and add the code from above. So your coding window
will look like this:

An IF Statement in C# .NET

Run your programme and click the button. You should see the message box.
Now halt the programme and change this line:

bool buttonClicked = true;

to this

bool buttonClicked = false;

So the only change is from true to false. Run your programme again, and click
the button. What happens? Nothing!

The reason that nothing happens is that our IF Statement is checking for
a value of true:

if (buttonClicked == true)

C# will only execute the code between the curly brackets IF, and only IF,
buttonClicked has a value of true. Since you changed the value to false, it
doesn’t bother with the MessageBox in between the curly brackets, but moves
on instead.

 

C# Else

You can also say what should happen if the answer was false. All you need
to do is make use of the else word. You do it like this:

if (buttonClicked = = true)
{

}
else
{

}

So you just type the word else after the curly brackets of the IF
Statement. And then add another pair of curly brackets. You then write your
code for what should happen if the IF Statement was false. Change your code
to this:

if (buttonClicked = = true)
{

MessageBox.Show(“buttonClicked has a value of true”);

}
else
{

MessageBox.Show(“buttonClicked has a value of false”);

}

So the whole thing reads:

“IF it’s true that buttonClicked has a value of
true, do one thing. If it’s not true, do another thing.”

Run your programme, and click the button. You should see the second MessageBox
display. Halt the programme and change the first line back to true.
So this:

bool buttonClicked = true;

instead of this:

bool buttonClicked = false;

Run the programme again, and click the button. This time, the first message
box will display.

The whole point of using IF ..Else Statements, though, is to execute one
piece of code instead of some other piece of code.

You can also extend the IF statement and add an else … if part.
This will be useful in our calculator programme. Click below to continue the
lessons.

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