Master C# Programming From Scratch

Control Flow Statements

Decision Making in programming is similar to decision making in real life. In programming too, a certain block of code needs to be executed when some condition is fulfilled. A programming language uses control statements to control the flow of execution of program based on certain conditions. Below are some decision-making statements.

Decision Making Statements

1. if Statement

   The if statement checks the given condition. If the condition evaluates to be true then the block of code/statements will execute otherwise not.

   Syntax

   C#

   if (condition)
   {
       // code to be executed
   }

   Note: If the curly brackets { } are not used with if statements then the statement just next to it is only considered associated with the if statement.

   Example

   C#

   using System;
    
   string name = "CIIT";
   
   // Using if statement
   if (name == "CIIT")
   {
       Console.WriteLine("Welcome to CIIT Training Institute ❤️👨‍🏫..!");
   }

   Try It

   When to use: Use an if statement when you want to execute code only when a particular condition is true.

2. if-else Statement

   Use this when we want one action to happen if the condition is true, and an alternative action to happen if it is false.

   Example

   C#

   using System;
    
   int num = 20;
   
   if (num % 2 == 0)
   {
       Console.WriteLine($"The number {num} is an even.");
   }
   else
   {
       Console.WriteLine($"The number {num} is an odd.");
   }

   Try It

   Real-World Example: An application can use if-else to check whether a candidate is eligible or not eligible based on their age or marks.

3. else if Statement (Multiple Conditions)

   If you need to test multiple distinct conditions, you can chain them using else if. The computer checks them in order and runs the code for the first condition that evaluates to true.

   Example

   C#

   using System;
    
   int percentage = 85;
   
   if (percentage >= 80)
   {
       Console.WriteLine("Grade: Excellent");
   }
   else if (percentage >= 60)
   {
       Console.WriteLine("Grade: Good"); // This will execute
   }
   else if (percentage >= 40)
   {
       Console.WriteLine("Grade: Average");
   }
   else
   {
       Console.WriteLine("Grade: Poor"); // Fail if no conditions match
   }

   Try It

   Important: The conditions are checked from top to bottom. Once a condition becomes true, its block executes and the remaining else if conditions are skipped.

4. Combining Conditions with Logical Operators

   We can check multiple conditions inside a single if statement using logical operators:

   • && (AND): Both conditions must be true.
   • || (OR): At least one condition must be true.
   • ! (NOT): Reverses the truth of the condition.

   Example

   C#

   using System;
    
   int a = 10;
   int b = 20;
   int c = 30;
   
   if (a > b && a > c)
   {
       Console.WriteLine($"{a} is greatest");
   }
   else if (b > a && b > c)
   {
       Console.WriteLine($"{b} is greatest");
   }
   else if (a == b && b > c && c == a)
   {
       Console.WriteLine("all are equal");
   }
   else
   {
       Console.WriteLine($"{c} is greatest");
   }

   Try It

   Example: Logical operators are useful when a decision depends on more than one condition.

Switch Case Statement

In C#, the switch statement is a control flow structure used to execute a specific block of code out of multiple choices. It is a cleaner, more readable alternative to an if-else if ladder when you are comparing one variable against a list of concrete values.

Traditional switch Statement

The traditional switch evaluates a variable (the expression) and matches it against various case labels.

Example

using System;
 
string priority = "High";

switch (priority)
{
    case "Low":
        Console.WriteLine("Fix within 7 days.");
        break; // Exits the switch block

    case "Medium":
        Console.WriteLine("Fix within 48 hours.");
        break;

    case "High":
        Console.WriteLine("Fix immediately!");
        break;

    default:
        Console.WriteLine("Unknown priority level.");
        break;
}

using System;
 
char grade = 'B';

switch (grade)
{
    case 'A':
    case 'B':
    case 'C':
        Console.WriteLine("You passed!");
        break;

    case 'D':
    case 'F':
        Console.WriteLine("You failed.");
        break;

    default:
        Console.WriteLine("Invalid grade.");
        break;
}

using System;
 
int dayNumber = 3;

// Elegant, single-statement evaluation
string dayName = dayNumber switch
{
    1 => "Monday",
    2 => "Tuesday",
    3 => "Wednesday",
    4 => "Thursday",
    5 => "Friday",
    _ => "Weekend / Unknown" // The discard pattern (default)
};

Console.WriteLine(dayName); // Outputs: Wednesday

using System;
 
class Circle
{
    public double Radius { get; set; }

    public Circle(double radius)
    {
        Radius = radius;
    }
}

class Rectangle
{
    public double Width { get; set; }
    public double Height { get; set; }

    public Rectangle(double width, double height)
    {
        Width = width;
        Height = height;
    }
}

class Program
{
    static void Main()
    {
        object shape = new Circle(5);

        switch (shape)
        {
            case Circle c:
                Console.WriteLine($"Circle with radius {c.Radius}");
                break;

            case Rectangle r:
                Console.WriteLine($"Rectangle of {r.Width}x{r.Height}");
                break;

            case null:
                Console.WriteLine("Shape is null.");
                break;
        }
    }
}

using System;
int marks = 75;

if (marks >= 80)
{
    Console.WriteLine("Grade: A");
}
else if (marks >= 60)
{
    Console.WriteLine("Grade: B");
}
else if (marks >= 40)
{
    Console.WriteLine("Grade: C");
}
else
{
    Console.WriteLine("Fail");
}