In this tutorial, we will learn how to use if, if…else, if…else if statement in C# to control the flow of our program’s execution.
C# supports the usual logical conditions from mathematics:
Testing a condition is unavoidable in programming. We will frequently confront circumstances where we need to test conditions (whether it is true or false) to control the flow of program. These conditions might be influenced by user’s input, time factor, current environment where the program is running, and so on
In this tutorial, we’ll learn to test conditions using if statement in C#.
In this article, you will learn-
C# if (if-then) Statement
C# if-then statement will execute a block of code if the given condition is true. The syntax of if-then statement in C# is:
if (boolean-expression)
{
// statements executed if boolean-expression is true
}
• The boolean-expression will return either true or false.
• If the boolean-expression returns true, the statements inside the body of if ( inside {…} ) will be executed.
• If the boolean-expression returns false, the statements inside the body of if will be disregarded.
For instance,
if (number < 5)
{
number += 5;
}
In this example, the statement
number += 5;
will be executed just if the value of number is less than 5.
Remember the += operator?
How if statement works?
Example 1: C# if Statement
using System;
namespace Conditional
{
class IfStatement
{
public static void Main(string[] args)
{
int number = 2;
if (number < 5)
{
Console.WriteLine("{0} is less than 5", number);
}
Console.WriteLine("This statement is always executed.");
}
}
}
At the point when we run the program, the output will be:
2 is less than 5 This statement is always executed.
The value of number is introduced to 2. So the expression number < 5 is assessed to true. Consequently, the code inside the if block are executed. The code after the if statement will consistently be executed irrespective to the expression.
Presently, change the value of number to something greater than 5, say 10. At the point when we run the program the output will be:
This statement is always executed.
The expression number < 5 will return false, subsequently the code inside if block will not be executed.
C# if…else (if-then-else) Statement
The if statement in C# may have an optional else statement. The block of code inside the else statement will be executed if the expression is assessed to false.
The syntax of if…else statement in C# is:
if (boolean-expression)
{
// statements executed if boolean-expression is true
}
else
{
// statements executed if boolean-expression is false
}
For instance,
if (number < 5)
{
number += 5;
}
else
{
number -= 5;
}
In this example, the statement
number += 5;
will be executed just if the value of number is less than 5.
The statement
number -= 5;
will be executed if the value of number is greater than or equivalent to 5.
How if…else Statement works?
Example 2: C# if…else Statement
using System;
namespace Conditional
{
class IfElseStatement
{
public static void Main(string[] args)
{
int number = 12;
if (number < 5)
{
Console.WriteLine("{0} is less than 5", number);
}
else
{
Console.WriteLine("{0} is greater than or equal to 5", number);
}
Console.WriteLine("This statement is always executed.");
}
}
}
At the point when we run the program, the output will be:
12 is greater than or equal to 5 This statement is always executed.
Here, the value of number is initialized to 12. So the expression number < 5 is assessed to false. Thus, the code inside the else block are executed. The code after the if..else statement will consistently be executed irrespective to the expression.
Presently, change the value of number to something less than 5, say 2. At the point when we run the program the output will be:
2 is less than 5 This statement is always executed.
The expression number < 5 will return true, consequently the code inside if block will be executed.
C# if…else if (if-then-else if) Statement
At the point when we have just one condition to test, if-then and if-then-else statement works fine. However, imagine a scenario in which we have a various condition to test and execute one of the many block of code.
For such case, we can use if..else if statement in C#. The syntax for if…else if statement is:
if (boolean-expression-1)
{
// statements executed if boolean-expression-1 is true
}
else if (boolean-expression-2)
{
// statements executed if boolean-expression-2 is true
}
else if (boolean-expression-3)
{
// statements executed if boolean-expression-3 is true
}
.
.
.
else
{
// statements executed if all above expressions are false
}
The if…else if statement is executed from the top and bottom. As soon as a test expression is true, the code within that if ( or there will be consequences if ) block is executed. At that point the control leaps out of the if…else if block.
On the off chance that none of the expression is true, the code inside the else block is executed.
Example 3: C# if…else if Statement
using System;
namespace Conditional
{
class IfElseIfStatement
{
public static void Main(string[] args)
{
int number = 12;
if (number < 5)
{
Console.WriteLine("{0} is less than 5", number);
}
else if (number > 5)
{
Console.WriteLine("{0} is greater than 5", number);
}
else
{
Console.WriteLine("{0} is equal to 5");
}
}
}
}
At the point when we run the program, the output will be:
12 is greater than 5
The value of number is introduced to 12. The first test expression number < 5 is false, so the control will move to the else if block. The test expression number > 5 is true thus the block of code inside else if will be executed.
Also, we can change the value of number to modify the flow of execution.
Nested if…else Statement
An if…else statement can exist inside another if…else statement. Such statements are called nested if…else statement.
The general structure of nested if…else statement is:
if (boolean-expression)
{
if (nested-expression-1)
{
// code to be executed
}
else
{
// code to be executed
}
}
else
{
if (nested-expression-2)
{
// code to be executed
}
else
{
// code to be executed
}
}
Nested if statements are for the most part used when we need to test one condition followed by another. In a nested if statement, if the external if statement returns true, it enters the body to check the inner if statement.
Example 4: Nested if…else Statement
The accompanying program computes the largest number among 3 numbers using nested if…else statement.
using System;
namespace Conditional
{
class Nested
{
public static void Main(string[] args)
{
int first = 7, second = -23, third = 13;
if (first > second)
{
if (firstNumber > third)
{
Console.WriteLine("{0} is the largest", first);
}
else
{
Console.WriteLine("{0} is the largest", third);
}
}
else
{
if (second > third)
{
Console.WriteLine("{0} is the largest", second);
}
else
{
Console.WriteLine("{0} is the largest", third);
}
}
}
}
}
At the point when we run the program, the output will be:
13 is the largest
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