There are three types of conditional statements using if and else keywords. A simple if statement, if else statement and then there is if else if statement.

C# If

If statement in C# is used to evaluate a set of statements conditionally based on an expression that evaluates to true or false.

Syntax

The syntax of C# If statement is:

if(boolean_expression) {
     /* statement(s) */
 }

The boolean_expression provided in the parenthesis after if keyword should evaluate to a boolean value, either True of False. If it evaluates to True, then the statement(s) inside the if block are executed. If the boolean_expression evaluates to False, then the statement(s) are not executed.

Example – C# If

In the following example, there are three if blocks demonstrating how an if statement is executed under different conditional evaluations.

Program.cs

using System;

namespace CSharpExamples
{
    class Program
    {
        static void Main(string[] args)
        {
            int a=1;
            int b=2;

            if(a==1){
                Console.WriteLine("a is 1.");    
            }

            if(a==b){
                Console.WriteLine("a is equal to b.");    
            }

            if(a!=b){
                Console.WriteLine("a is not equal to b.");    
            }
        }
    }
}

Output

PS D:\workspace\csharp\HelloWorld> dotnet run
a is 1.
a is not equal to b.

What happened in this C# If Statement Example?

There are three independent if blocks here.

In the first if block, the condition a==1 evaluates to True. Therefore, the statements inside that if block are executed.

Coming to second if block example, the condition a==b evaluates to False and hence the statements inside this if block are not executed.

Finally in the third if block, the condition a!=b returns True. And the statements inside this if block are executed.

C# If..Else Statement

Program.cs

using System;

namespace CSharpExamples
{
    class Program
    {
        static void Main(string[] args)
        {
            int a=1;

            if(a==0){
                Console.WriteLine("a is 0.");    
            } else if(a==1){
                Console.WriteLine("a is 1.");    
            } else if(a==2){
                Console.WriteLine("a is 2.");    
            }
        }
    }
}

Output

PS D:\workspace\csharp\HelloWorld> dotnet run
a is 1.

What happened in this C# If..Else Example?

In the above example, first if condition a==0 is checked. It evaluates to False. Then, the control moves to the next if block a==1 in the if-else-if ladder. The condition evaluates to True. Hence, the statements inside that if block are executed. The control then comes out of the whole if-else-if ladder without executing subsequent else-if blocks.

C# If..Else If Statement

Program.cs

using System;

namespace CSharpExamples
{
    class Program
    {
        static void Main(string[] args)
        {
            int a=1;
            int b=2;

            if(a==1){
                Console.WriteLine("a is 1.");    
            }

            if(a==b){
                Console.WriteLine("a is equal to b.");    
            }

            if(a!=b){
                Console.WriteLine("a is not equal to b.");    
            }
        }
    }
}

Output

PS D:\workspace\csharp\HelloWorld> dotnet run
a is 1.
a is not equal to b.

Conclusion

In this C# Tutorial, we learned the syntax and usage of decision making statements: If, If-Else and If-Else-If.