C# .NET

C# Operators

 

 

You’ve already met one Conditional Operator, the double equals
sign ( == ). You use this in IF Statement when you want to check if a variable
“has a value of” something:

if ( myVariable == 10)
{

//EXECUTE SOME CODE HERE

}

So the above line reads, “IF whatever is inside of myVariable
has a value of 10, execute some code.”

Other Conditional Operators you’ll use when you’re coding are these:

C# Operators

Because you need to learn these Operators, let’s get some practice with them.

Start a new project. Add two text boxes and a button to your form. Resize the
text boxes and type 8 as the Text property for the first text box, and 7 as
the Text property for the second text box. Set the Text property for the button
to the word “Compare”. Your form will then look like this:

Design this form in C#

Double click the button to get at the coding window. What we’ll do is to get
the numbers from the text boxes and test and compare them. So the first thing
to do is to set up some variables:

int firstNumber;
int secondNumber;

Then get the text from the text boxes and store them in the variables (after
converting them to integers first.)

firstNumber = int.Parse(textBox1.Text);
secondNumber = int.Parse(textBox2.Text);

What we want to do now is to compare the two numbers. Is the first number bigger
than the second number? To answer this, we can use an IF Statement, along with
one of our new Conditional Operators. So add this to your code:

if (firstNumber > secondNumber)
{

MessageBox.Show(“The first number was greater than
the second number”);

}

Your coding window will then look like this (our message box above is only
on two lines because it can’t all fit on this page):

the Greater Than operator in C#

So in between the round brackets after if, we have our two variables.
We’re then comparing the two and checking to see if one is Greater Than
( > ) the other. If firstNumber is Greater Than secondNumber
then the message box will display.

Run your programme and click your button. You should see the message box display.
Type a 6 in the first text box, and click the button again. The message box
won’t display. It won’t display because 6 is not greater than 7. The message
box code is inside of the curly brackets of the IF Statement. And the IF Statement
only gets executed if firstNumber is Greater Than secondNumber. If it’s not,
C# will just move on to the next line. You haven’t got any more lines, so C#
is finished.

Stop your programme and go back to your code. Add a new if statement below
your first one:

if (firstNumber < secondNumber)
{

MessageBox.Show(“The first number was less than the
second number”);

}

Again, our message box above is spread over two lines because there’s not enough
room for it on this page. Your message box should go on one line. But the code
is just about the same! The thing we’ve changed is to use the Less Than
symbol ( < ) instead of the Greater Than symbol ( > ). We’ve also
changed the text that the message box displays.

Run your programme, and type a 6 in the first text box. You should see your
new message box display. Now type an 8 in the first text box, and click your
button. The first message box will display. Can you see why? If your programme
doesn’t work at all, make sure it is like ours in the image below:

Less Than in C# .NET

With your programme still running, type a 7 in the first box. You will then
have a 7 in both text boxes. Before you click your button, can you guess what
will happen?

The reason that nothing happens at all is because you haven’t written any code
to say what should happen if both numbers are equal. For that, try these new
symbols:

>= (Greater Than
or Equal to)

And these ones

<= (Less Than or Equal to)

Try these new Conditional Operators in place of the ones you already have.
Change the text for your message boxes to suit. Run your code again. When you
click the button, both message boxes will display, one after the other. Can
you see why this happens?

Another Conditional Operator to try is Not Equal To ( != ). This is
an exclamation mark followed by an equals sign. It is used like this:

if (firstNumber != secondNumber )
{

//SOME CODE HERE

}

So, “IF firstNumber is not equal to secondNumber execute some code.”

You can even use the exclamation mark by itself. You do this when you want
to test for a false value between the round brackets after if. It’s mostly used
with Boolean values. Here’s an example:

bool testValue = false;

if (!testValue)
{

MessageBox.Show(“Value was false”);

}

So the exclamation mark goes before the Boolean value you want to test. It
is a shorthand way of saying “If the Boolean value is false”. You
can write the line like this instead:

if (testValue == false)

But experienced programmers just use the exclamation mark instead. It’s called
the NOT Operator. Or the “IF NOT true” Operator.

Try not to worry if you don’t have a thorough grasp of all the Conditional
Operators yet – you’ll get the hang of them as you go along. But try the next
exercise.

 

Exercise F
Write a small programme with a text box and a button. Add a label to ask people
to enter their age. Use Conditional Logic to test how old they are. Display
the following messages, depending on how old they are:

Less than 16: “You’re still a youngster.”
Over 16 but under 25: “Fame beckons!”
Over 25 but under 40: “There’s still time.”
Over 40: “Oh dear, you’ve probably missed it!”

Only one message box should display, when you click the button. Here’s some
code to get you started:

int age;

age = int.Parse(textBox1.Text);

if (age < 17)
{

MessageBox.Show(“Still a youngster.”);

}

For the others, just add more IF Statements, and more Condition Operators.

 

AND and OR

The final two Operators we’ll have a look at are these:

&& (And)
||(Or)

These two are known as Logical Operators, rather than Conditional Operators
(so is the NOT operator).

The two ampersand together (&&) mean AND. You use them like this:

bool isTrue = false;
bool isFalse = false;

if ( isTrue == false && isFalse == false )
{

}

You use the AND operator when you want to check more than one value at once.
So in the line above, you’re checking if both values are false. If and ONLY
if both of your conditions are met will the code between curly brackets get
executed. In the code above, we’re saying this:

“If isTrue has a value of false AND if isFalse
has a value of false then and only then executed the code between curly brackets.”

If isTrue is indeed true, for example, then any code between curly brackets
won’t get executed – they both have to be false, in our code.

You can test for only one condition of two being met. In which, use the OR
( | | ) operator. The OR operators is two straight lines. These can be found
above the back slash character on a British keyboard, which is just to the left
of the letter “Z”. (The | character is known as the pipe character.)
You use them like this:

bool isTrue = false;
bool isFalse = false;

if ( isTrue == false || isFalse == false )
{

}

We’re now saying this:

“If isTrue has a value of false OR if isFalse
has a value of false then and only then executed the code between curly brackets.”

If just one of our variables is false, then the code in between curly brackets
will get executed.

If all that sounds a bit complicated, don’t worry about it – you’ll get more
practice as we go along

 

In the next section, we’ll have a look at loops, which are another crucial
hurdle to overcome in programming. By the end of the section, you’ll have written
your own times table programme.

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