Computer Programming
C#
Lec.05
Salem Belgurzi
Topics
• C# Conditions and If Statements
• The if Statement
• The else Statement
• The else if Statement
• Short Hand If...Else
• C# Switch Statements
C# Conditions and If Statements
• C# supports the usual logical conditions from mathematics:
• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b
• Equal to a == b
• Not Equal to: a != b
• You can use these conditions to perform different actions for different
decisions.
C# Conditions and If Statements
• C# has the following conditional statements:
• Use if to specify a block of code to be executed, if a specified condition is
true
• Use else to specify a block of code to be executed, if the same condition
is false
• Use else if to specify a new condition to test, if the first condition is false
• Use switch to specify many alternative blocks of code to be executed
The if Statement
• Use the if statement to specify a block of C# code to be
executed if a condition is True.
if (condition)
{
// block of code to be executed if the condition is True
}
• Note that if is in lowercase letters. Uppercase letters (If or IF)
will generate an error.
The if Statement
• In the example below, we test two values to find out if 20 is
greater than 18. If the condition is True, print some text:
if (20 > 18)
{
Console.WriteLine("20 is greater than 18");
}
The if Statement
• You can also test variables:
int x = 20;
int y = 18;
if (x > y)
{
Console.WriteLine("x is greater than y");
}
• In the example above we use two variables, x and y, to test
whether x is greater than y (using the > operator). As x is 20,
and y is 18, and we know that 20 is greater than 18, we print
to the screen that "x is greater than y".
The else Statement
• Use the else statement to specify a block of code to be
executed if the condition is False.
if (condition)
{
// block of code to be executed if the condition is True
}
else
{
// block of code to be executed if the condition is False
}
The else Statement
• In the example below, time (20) is greater than 18, so the
condition is False. Because of this, we move on to the else
condition and print to the screen "Good evening". If the time
was less than 18, the program would print "Good day"..
int time = 20;
if (time < 18)
{
Console.WriteLine("Good day.");
}
else
{
Console.WriteLine("Good evening.");
}
// Outputs "Good evening."
The else if Statement
• Use the else if statement to specify a new condition if the first
condition is False.
if (condition1)
{
// block of code to be executed if condition1 is True
}
else if (condition2)
{
// block of code to be executed if the condition1 is false and condition2 is True
}
else
{
// block of code to be executed if the condition1 is false and condition2 is False
}
The else if Statement
• Example:
int time = 22;
if (time < 10)
{
Console.WriteLine("Good morning.");
}
else if (time < 20)
{
Console.WriteLine("Good day.");
}
else
{
Console.WriteLine("Good evening.");
}
// Outputs "Good evening."
Short Hand If...Else (Ternary Operator)
• There is also a short-hand if else, which is known as the
ternary operator because it consists of three operands. It
can be used to replace multiple lines of code with a single
line. It is often used to replace simple if else statements:
variable = (condition) ? expressionTrue : expressionFalse;
Short Hand If...Else (Ternary Operator)
• Instead of writing:
• Example:
int time = 20;
if (time < 18)
{
Console.WriteLine("Good day.");
}
else
{
Console.WriteLine("Good evening.");
}
Short Hand If...Else (Ternary Operator)
• You can simply write:
int time = 20;
string result = (time < 18) ? "Good day." : "Good evening.";
Console.WriteLine(result);
C# Switch Statements
• Use the switch statement to select one of many code blocks
to be executed.
switch(expression)
{
case x:
// code block
break;
case y:
// code block
break;
default:
// code block break; }
C# Switch Statements
• This is how it works:
•The switch expression is evaluated once
•The value of the expression is compared with the
values of each case
•If there is a match, the associated block of code is
executed
C# Switch Statements
• The break Keyword:
• When C# reaches a break keyword, it breaks out of the
switch block.
• This will stop the execution of more code and case testing
inside the block.
• When a match is found, and the job is done, it's time for a
break. There is no need for more testing.
• A break can save a lot of execution time because it "ignores"
the execution of all the rest of the code in the switch block.
C# Switch Statements
• The example below uses the weekday number to
calculate the weekday name:
int day = 4;
C# Switch Statements
switch (day) {
case 1:
Console.WriteLine("Sunday");
break;
case 2:
Console.WriteLine("Monday");
break;
case 3:
Console.WriteLine("Tuesday");
break;
case 4:
Console.WriteLine("Wednesday");
break;
case 5:
Console.WriteLine("Thursday");
break;
case 6:
Console.WriteLine("Friday");
break;
Case 7:
Console.WriteLine("Saturday");
break;
}
C# Switch Statements
• The default Keyword
• The default keyword is optional and specifies some code to
run if there is no case match.
C# Switch Statements
• Example:
int day = 4;
switch (day)
{
case 6:
Console.WriteLine("Today is Friday.");
break;
case 7:
Console.WriteLine("Today is Saturday.");
break;
default:
Console.WriteLine("Looking forward to the Weekend.");
break;
}
// Outputs "Looking forward to the Weekend."
