Csharp/CSharp Tutorial/Statement/If

A nested if statement

<source lang="csharp">class MainClass {

 public static void Main()
 {
   int intValue = 1500;
   string stringValue = " ";
   if (intValue < 1000)
   {
     System.Console.WriteLine("intValue < 1000");
   }
   else
   {
     System.Console.WriteLine("intValue >= 1000");
     if (stringValue == "closed")
     {
       System.Console.WriteLine("closed");
     }
   }
 }

}</source>

intValue >= 1000

bool values in if statement

<source lang="csharp">using System;

class Example {

 public static void Main() { 
   bool b; 

   b = false; 
   Console.WriteLine("b is " + b); 
   b = true; 
   Console.WriteLine("b is " + b); 

   // a bool value can control the if statement 
   if(b) 
      Console.WriteLine("This is executed."); 

   b = false; 
   if(b) 
      Console.WriteLine("This is not executed."); 

 } 

}</source>

b is False
b is True
This is executed.

Demonstrate the if statement

<source lang="csharp">using System;

class MainClass {

 public static void Main() {  
   int a, b, c;  
 
   a = 2;  
   b = 3;  
 
   if(a < b) 
       Console.WriteLine("a is less than b"); 

   if(a == b) 
       Console.WriteLine("you won"t see this");  

   Console.WriteLine(); 

   c = a - b;

   Console.WriteLine("c is",c); 
   if(c >= 0) 
        Console.WriteLine("c is non-negative"); 
   if(c < 0) 
        Console.WriteLine("c is negative"); 

   Console.WriteLine(); 

   c = b - a;
   Console.WriteLine("c is",c); 
   if(c >= 0) 
       Console.WriteLine("c is non-negative"); 
   if(c < 0) 
       Console.WriteLine("c is negative"); 
 }  

}</source>

a is less than b
c is
c is negative
c is
c is non-negative

Determine if a value is positive, negative, or zero

<source lang="csharp">using System;

class MainClass {

 public static void Main() { 
   int i; 

   for(i=-5; i <= 5; i++) { 

     Console.Write("Testing " + i + ": "); 

     if(i < 0) 
         Console.WriteLine("negative"); 
     else if(i == 0) 
         Console.WriteLine("no sign"); 
     else 
         Console.WriteLine("positive"); 
   } 
 } 

}</source>

Testing -5: negative
Testing -4: negative
Testing -3: negative
Testing -2: negative
Testing -1: negative
Testing 0: no sign
Testing 1: positive
Testing 2: positive
Testing 3: positive
Testing 4: positive
Testing 5: positive

If a value is positive or negative

The semicolon signals the end of a statement.

<source lang="csharp">using System;

class MainClass {

 public static void Main() { 
   int i; 

   for(i=-5; i <= 5; i++) { 
     Console.Write("Testing " + i + ": "); 

     if(i < 0) 
        Console.WriteLine("negative"); 
     else 
        Console.WriteLine("positive"); 
   } 
 } 

}</source>

Testing -5: negative
Testing -4: negative
Testing -3: negative
Testing -2: negative
Testing -1: negative
Testing 0: positive
Testing 1: positive
Testing 2: positive
Testing 3: positive
Testing 4: positive
Testing 5: positive

if statement with || and &&

<source lang="csharp">using System; class MainClass {

 static void Main(string[] args)
 {
   int a = 5, b = 5, c = 10;
   if (a == b)
     Console.WriteLine(a);
   if ((a > c) || (a == b))
     Console.WriteLine(b);
   if ((a >= c) && (b <= c))
     Console.WriteLine(c);
 }

}</source>

5
5

Relational operators that can be used in a conditional expression.

Operator Meaning < Less than <= Less than or equal > Greater than >= Greater than or equal == Equal to != Not equal

The if Statement

You can selectively execute part of a program through the if statement.

Its simplest form is shown here:

<source lang="csharp">if(condition)

  statement;</source>

Use an if statement that executes a block

A code block is a grouping of two or more statements. This is done by enclosing the statements between opening and closing curly braces.

<source lang="csharp">class MainClass {

 public static void Main()
 {
   int smallNumber = 5;
   int bigNumber = 100;
   if (bigNumber < smallNumber)
   {
     System.Console.Write(bigNumber);
     System.Console.Write(" is less than ");
     System.Console.Write(smallNumber);
   }
   else
   {
     System.Console.Write(smallNumber);
     System.Console.Write(" is less than ");
     System.Console.Write(bigNumber);
   }
 }

}</source>

5 is less than 100