The if statement evaluates its condition expression to determine whether to execute the if-body.
Optionally, an else clause can immediately follow the if body, providing code to execute when the condition is false.
Making the else-body another if statement creates the common cascade of if, else if, else if, else if, else statements
if Statement
This is the syntax of the if statement
if(condition)
{
//code to be executed
}
Example
If the variable x is greater than 10 display a message, it is.
using System;
public class Program
{
public static void Main()
{
int x = 20;
if (x >= 10)
{
Console.WriteLine("x is Greater than 10");
}
Console.WriteLine("Press Enter Key to Exit..");
Console.ReadLine();
}
}
You should see the following
x is Greater than 10 Press Enter Key to Exit..
Change the above example so that if (x <= 10) and see what happens
if-else Statement
Use the else statement to specify a block of code t that will be executed if the condition is False.
This is the syntax of the if-else statement
if(condition)
{
//code if condition is true
}
else
{
//code if condition is false
}
lets see an example of this
Example
using System;
public class Program
{
public static void Main()
{
int x = 20;
if (x <= 10)
{
Console.WriteLine("x is greater than 10");
}
else
{
Console.WriteLine("x is less than 10");
}
Console.WriteLine("Press Enter Key to Exit..");
Console.ReadLine();
}
}
You should see the following
x is less than 10 Press Enter Key to Exit..
If else-if Example
Use the else if statement to specify a new condition to be checked if the first condition is False.
This is the syntax of the if else-if statement
if(condition1)
{
//code to be executed if condition1 is true
}
else if(condition2)
{
//code to be executed if condition2 is true
}
else if(condition3)
{
//code to be executed if condition3 is true
}
...
else
{
//code to be executed if all the conditions are false
}
A similar example as before
using System;
public class Program
{
public static void Main()
{
int x = 10;
if (x > 10)
{
Console.WriteLine("x is greater than 10");
}
else if(x < 10)
{
Console.WriteLine("x is less than 10");
}
else
{
Console.WriteLine("x is 10");
}
Console.WriteLine("Press Enter Key to Exit..");
Console.ReadLine();
}
}
Which will result in
x is 10 Press Enter Key to Exit..
Here is another example, this is your fairly typical console grade program where a user inputs a grade and you use an if else-if to display a message to the user depending on the grade.
using System;
public class Program
{
public static void Main()
{
Console.WriteLine("Enter a number to check grade:");
int num = Convert.ToInt32(Console.ReadLine());
if (num <0 || num >100)
{
Console.WriteLine("wrong number");
}
else if(num >= 0 && num < 50){
Console.WriteLine("Fail");
}
else if (num >= 50 && num < 60)
{
Console.WriteLine("D Grade");
}
else if (num >= 60 && num < 70)
{
Console.WriteLine("C Grade");
}
else if (num >= 70 && num < 80)
{
Console.WriteLine("B Grade");
}
else if (num >= 80 && num < 90)
{
Console.WriteLine("A Grade");
}
else if (num >= 90 && num <= 100)
{
Console.WriteLine("A+ Grade");
}
}
}
Here is a run of this program
Enter a number to check grade: 74 B Grade
Nested if…else Statement
You can also nest if…else statements, lets look at the syntax
if (condition1)
{
if (condition2)
{
// code to be executed if condition2 is true
}
else
{
// code to be executed if condition2 is false
}
}
else
{
if (condition3)
{
// code to be executed if condition3 is true
}
else
{
// code to be executed if condition3 is true
}
}
Nested if statements are used when we have to test one condition followed by another. In a nested if statement, if the outer if statement returns true, it enters the body to check the inner if statement.
Lets see an example of this
using System;
public class Program
{
public static void Main()
{
int x = 10, y = 30;
if (x > y)
{
if (x >= 20)
{
Console.WriteLine("x is greater than or equal to 10");
}
else
{
Console.WriteLine("x is less than 10");
}
}
else
{
if (y <= 20)
{
Console.WriteLine("y is less than or equal to 20");
}
else
{
Console.WriteLine("y is greater than 20");
}
}
Console.WriteLine("Press Enter Key to Exit..");
Console.ReadLine();
}
}
Run this and you will see the following
y is greater than 20 Press Enter Key to Exit..