In this post we explain about all four conditional construct with the help of examples If
you are reading our C# posts first time we will suggest you to read our
previous post to better understand the concept, if you already had or you know
the concept and want to know about conditional construct then start reading.
But first we should understand about Boolean value.
Boolean Variable and Operator
C#
provide a data type called bool. A
variable of bool data type can only
hold two value either false or true. For example:
bool car;
car = false;
Console.WriteLine(car); // print False on console screen
In
the preceding example a variable of bool
data type car is declared which has
been assigned a value false, and WriteLine method of the console class is used to print the value
of car variable.
Similarly a Boolean operator is an
operator that evaluate a statement whose result is either true or false. For
example:
int a, b;
bool result;
a = 10;
b = 8;
result = (a != b);//evaluate the expression on
right and assign its result to the variable on left
Console.WriteLine(result);//
print the value of result on console screen
In the preceding example, we have declared
two variable a, and b of integer data type and assigned
values 10 to a, and 8 to b. In the fifth line we are checking
whether the value of variable a is
equals to the value of variable b, to
check it we are using a comparison operator not equals to that can only have two values
either true or false, and then assigning the outcome to the result variable of
Boolean data type that again can have only two value true, or false.
NOTE: In the
preceding example the result variable is of Boolean data type any other data
type will not support this statement and will give error because the
expression will return a Boolean value and only a Boolean variable can store bool value true or false.
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To
fully understand the concept of conditional constructs you should have the
knowledge of data types and variables. Click here to read about it in our post
Conditional construct
Conditional construct or conditional statement are used to make decision in your program consider an example of a traffic light you will stop your car when the light is red and go when it is green, so whether you will stop your car or go depend on the state of traffic light whether it is red or green. Whenever you find this type of situation in coding you can use conditional construct.
The
conditional construct will execute a particular block of statement based on the
condition you provide, the condition are of Boolean value , means an expression
will return either true or false value.
There
are four types of conditional construct in C#:
- if Statement.
- if….else statement.
- Nested if…else statement.
- Switch case statement.
The if statement
The if statement is followed by a BooleanExpression if the BooleanExpression evaluates to true the statement in the if the block will be executed but if the BooleanExpression evaluates to false, the execution of code will continue with whatever code is after that if block.
The syntax of if statement:
if (BooleanExpression)
{
Statement1;
Statement2;
}
If there is only a single
statement in your if block it is not necessary to enclose the if
block within curly braces (delimiters). Example:
if
(BooleanExpression)
Statement1; //Single statement
This code will work because it has only one statement in the if
block.
The if…else statement
The if...else
statement is same as the if statement but with the addition
of an else block. If the BooleanExpression in the if…else
block evaluate to false the statement in the else block will get executed. The
syntax for if…else construct or statement is:
if (BooleanExpression)
{
Statement1;
}
else
{
Statements1;
}
Consider an example where you want to accept a number from the user
and check if it’s an even number or odd, and print the result on the console
screen. The following code show you how to do this using the if…else
construct:
int a;
Console.WriteLine("Enter a number");
a = Convert.ToInt32(Console.ReadLine());
if ( a % 2 == 0 )
{
Console.WriteLine("You Entered an Even
Number");
}
else
{
Console.WriteLine("You Entered an Odd
Number");
}
So, in the preceding code we have declared
a variable a of integer data type then we used the ReadLine method of the console
class to accept input from user on line 3 the ReadLine method by
default accept data in string format so we used the Convert.ToInt32 method to convert it in integer format for our integer variable a in
the BooleanExpression
of the if block we use the modulus operator to check if the remainder is equals to 0 after
dividing the variable by 2 if it evaluates to true the code in the if block
will get executed if not the else block will get executed. See the output of
console screen below:
The nested if…else Statement
The if… else statement can also be nested inside each other. Means you can write an if…else statement inside an if block or the else block. Check the syntax below:
if (BooleanExpression)
{
Statement;
if (BooleanExpression)
{
Statement;
}
else
{
Statement;
}
Statement;
}
else
{
Statement;
}
For example think of a
situation where the user want to check his grade, for this he have to input his
name and student id if the input he gave was right then the grade will be shown on the console
screen else “Invalid Name Or ID” will be shown. For this he have to write the
following code:
string
name, studentId;
Console.WriteLine("Please Enter Your
Name");
name = Console.ReadLine();
Console.WriteLine("Please Enter Your
Student ID");
studentId = Console.ReadLine();
if
(name.ToUpper() == "ALEX")
{
if (studentId == "i396")
{
Console.WriteLine("Congratulations You
Got Grade A");
}
else
{
Console.WriteLine("Invalid Name or
ID");
}
}
In the preceding code we accept the name and student id of the user
and store it in the name and studentId variable which are of
string data type note that the ReadLine method accept string data
type by default so we don’t have to
convert the data type of our variables. In the sixth line we are using ToUpper()
method to convert the user input into uppercase letter, this small things are
really important in your code because you don’t know how the user will type his
name to fix this error we used the ToUpper() method. Then you can see that how use the
second if…else statement to validate the studentId. So this is how
you can use nested if…else block in this type of situation where you have to
evaluate multiple condition in your code. See the output below:
.bmp)
And the invalid input:
But this code can also be written with logical operators check the
code below:
string
name, studentId;
Console.WriteLine("Please Enter Your
Name");
name = Console.ReadLine();
Console.WriteLine("Please Enter Your
Student ID");
studentId = Console.ReadLine();
if
((name.ToUpper() == "ALEX")&&(studentId == "i396"))
{
Console.WriteLine("Congratulations You Got Grade A");
}
else
{
Console.WriteLine("Invalid Name or ID");
}
So in the preceding code
we used the logical operator to check both condition in the same
BooleanExpression, and it will give you the same result. To read about logical
operators click here
The switch…case Statement
Think of a situation where have to evaluate a variable for multiple values, like where a user want to open a particular hotel room based on the room number, if you used nested if…else you have write multiple if…else block and it will be time consuming and not a good coding practice. In this type of situation you can use switch…case construct. The switch case construct is used where you have evaluate a variable for multiple values the syntax of switch case is:
switch (controllingExpression)
{
case
constantExpression:
statements;
break;
case
constantExpression:
statements;
break;
case
constantExpression:
statements;
break
default:
statements;
break;
}
In the switch case statement the controllingExpression is
only evaluated once, the controllingExpression is the
variable you want to evaluate. If one of the constantExpression match
with the value given in the variable means the controllingExpression the
control will be passed to the statements of that matched case. The break
statement is used to stop the switch…case construct to prevent
the execution of remaining case structures. If none of the constantExpression
matched with the value of the controllingExpression the statement
under the default statement will run.
Let’s write the code on hotel room example were the user want to
open a room based on its room number:
int roomNumber;
Console.WriteLine("Enter your room number");
roomNumber = Convert.ToInt32(Console.ReadLine());
switch (roomNumber)
{
case 105:
Console.WriteLine("Wrong
room");
break;
case 106:
Console.WriteLine("Sorry
for disturbance, wrong room");
break;
case 107:
Console.WriteLine("Welcome
to your room");
break;
case 108:
Console.WriteLine("Hotel
staff room");
break;
default:
Console.WriteLine("Sorry
Invalid room number");
break;
}
Check
the outputs below:
The user entered 106.
The user entered 107.
The user entered 200.
The switch…case statement rules
There are some rules you should remember and follow while working with switch…case construct:
- The constant expression must be unique, means two constantExpression can’t have the same value.
- You can’t use every data type for the switch…case controllingExpression. Only int, char, or string can be used for any other data type like decimal and float you have to use if statement.
- If you are using int data type you have to write 5, for char data type you have to write ‘5’, and for string data type you have to write “5”. If you write 4 for string data type it will give you an error it must be written like “4”.
So start coding use this concept in your
code ask me about any problem you have while using this concepts on your
program in comments. Read our previous posts on C#
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