Decision making structures requires the programmer to specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

 

C# provides following types of decision-making statements –

 

1.      if statement

An if statement consists of a boolean expression followed by one or more statements.

 

Syntax:

The syntax of an if statement in C# is −

if(boolean_expression) {

   /* statement(s) will execute if the boolean expression is true */

}

If the boolean expression evaluates to true, then the block of code inside the if statement is executed. If boolean expression evaluates to false, then the first set of code after the end of the if statement (after the closing curly brace) is executed.

Example

using System;

 

namespace DecisionMaking {

   class Program {

      static void Main(string[] args) {

         /* local variable definition */

         int a = 10;

       

         /* check the boolean condition using if statement */

         if (a < 20) {

            /* if condition is true then print the following */

            Console.WriteLine("a is less than 20");

         }

         Console.WriteLine("value of a is: {0}", a);

         Console.ReadLine();

      }

   }

}

Output

When the above code is compiled and executed, it produces the following result −

a is less than 20

value of a is: 10

 

 

2.      if...else statement

An if statement can be followed by an optional else statement, which executes when the boolean expression is false.

Syntax:

The syntax of an if...else statement in C# is −

if(boolean_expression) {

   /* statement(s) will execute if the boolean expression is true */

} else {

   /* statement(s) will execute if the boolean expression is false */

}

If the boolean expression evaluates to true, then the if block of code is executed, otherwise else block of code is executed.

Example

using System;

namespace DecisionMaking {

   class Program {

      static void Main(string[] args) {

         /* local variable definition */

         int a = 100;

         /* check the boolean condition */

         if (a < 20) {

            /* if condition is true then print the following */

            Console.WriteLine("a is less than 20");

         }