A Complete Guide - Control Flow Statements in C#

Control Flow Statements in C# Explained in Detail

Conditional Statements

1. if Statement

   • The if statement is used for conditional execution of a block of code only if a specified boolean expression evaluates to true.

   if (condition) {
      // Code to execute if condition is true
   }
   

   • Example:

     int number = 5;
     if (number > 0) {
        Console.WriteLine("The number is positive.");
     }
     

2. if-else Statement

   • An extension of the if statement, where a block of code can be executed if the condition is not met (false).

   if (condition) {
      // Code to execute if condition is true
   } else {
      // Code to execute if condition is false
   }
   

   • Example:

     int number = -1;
     if (number > 0) {
        Console.WriteLine("The number is positive.");
     } else {
        Console.WriteLine("The number is negative or zero.");
     }
     

3. if-else-if Ladder

   • Allows multiple conditions to be evaluated sequentially.

   if (condition1) {
      // Code to execute if condition1 is true
   } else if (condition2) {
      // Code to execute if condition2 is true and condition1 is false
   } else {
      // Code to execute if all previous conditions are false
   }
   

   • Example:

     int grade = 85;
     if (grade >= 90) {
        Console.WriteLine("You got an A");
     } else if (grade >= 80) {
        Console.WriteLine("You got a B");
     } else if (grade >= 70) {
        Console.WriteLine("You got a C");
     } else {
        Console.WriteLine("Below average grade");
     }
     

4. switch Statement

   • Evaluates a single expression against a list of case labels and executes one set of statements based on the match.

   switch (expression) {
       case value1:
           // Code to execute if expression matches value1
           break;
       case value2:
           // Code to execute if expression matches value2
           break;
       default:
           // Code to execute if none of the above match
           break;
   }
   

   • Example:

     int day = 3;
     switch (day) {
         case 1:
             Console.WriteLine("Monday");
             break;
         case 2:
             Console.WriteLine("Tuesday");
             break;
         case 3:
             Console.WriteLine("Wednesday");
             break;
         default:
             Console.WriteLine("Unknown Day");
             break;
     }
     

Looping Statements

1. for Loop

   • Executes a block of code repeatedly based on a counter variable.

   for (initialization; condition; increment/decrement) {
      // Code to execute
   }
   

   • Example:

     for (int i = 0; i < 5; i++) {
        Console.WriteLine(i);
     }
     

2. foreach Loop

   • Iterates over elements in a collection like arrays, lists, or dictionaries.

   foreach (var element in collection) {
      // Code to execute for each element
   }
   

   • Example:

     string[] days = { "Monday", "Tuesday", "Wednesday" };
     foreach (var day in days) {
        Console.WriteLine(day);
     }
     

3. while Loop

   • Continues to execute as long as the provided condition is true.

   while (condition) {
      // Code to execute
   }
   

   • Example:

     int count = 0;
     while (count < 5) {
        Console.WriteLine(count);
        count++;
     }
     

4. do-while Loop

   • Similar to the while loop but guarantees execution at least once as the evaluation takes place after the first iteration.

   do {
      // Code to execute
   } while (condition);
   

   • Example:

     int count = 0;
     do {
        Console.WriteLine(count);
        count++;
     } while (count < 5);
     

Jump Statements

1. break Statement

   • Terminates the nearest enclosing loop or switch block.
   • Useful for exiting early when a specific condition is met.
   • Example inside a for loop:

     for (int i = 0; i < 10; i++) {
        if (i == 5) {
           break;
        }
        Console.WriteLine(i);
     }
     

   • Example inside a switch:

     switch (day) {
         case 1:
             Console.WriteLine("Monday");
             break;
         case 2:
             Console.WriteLine("Tuesday");
             break;
         default:
             Console.WriteLine("Unknown Day");
             break;
     }
     

2. continue Statement

   • Skips the current iteration and begins the next iteration of the nearest enclosing loop.
   • Example in a for loop:

     for (int i = 0; i < 10; i++) {
        if (i % 2 == 0) {
           continue;
        }
        Console.WriteLine(i);
     }
     

   Output: Odd numbers from 0 to 9 will be printed.

3. goto Statement

   • Transfers control to a named label within the program.

   label:
   // Code to execute
   goto label;
   // More code
   

   • Discouraged: Typically avoided due to poor readability and maintainability.
   • Example:

     int i = 0;
     start:
     Console.WriteLine(i);
     i++;
     if (i < 5) {
        goto start;
     }
     

4. return Statement

   • Exits from a method and optionally returns a value to the caller.
   • Useful for terminating methods based on certain conditions.
   • Example:

     int Divide(int num1, int num2) {
        if (num2 == 0) {
           return 0; // Avoid division by zero
        }
        return num1 / num2;
     }
     

Exception Handling

1. try-catch Block

   • Used for structured error handling.
   • try blocks contain the code to monitor for exceptions.
   • catch blocks handle exceptions.

   try {
      // Code that might throw an exception
   } catch (ExceptionType1 ex) {
      // Handle type1 exceptions
   } catch (ExceptionType2 ex) {
      // Handle type2 exceptions
   } finally {
      // Code to run regardless of whether an exception occurred
   }
   

   • Example:

     try {
        int result = Divide(10, 0); // This raises an exception
     } catch (DivideByZeroException ex) {
        Console.WriteLine("Error: Division by zero");
     } finally {
        Console.WriteLine("Operation attempted.");
     }
     

2. throw Statement

   • Throws an exception explicitly.

   throw new ExceptionType("ErrorMessage");
   

   • Example:

     int Divide(int num1, int num2) {
        if (num2 == 0) {
           throw new DivideByZeroException("Denominator cannot be zero.");
        }
        return num1 / num2;
     }
     

Null Coalescing and Conditional Operators

1. null-coalescing Operator (??)

   • Provides a way to assign default values for nullable types or reference types.

   variable ?? defaultValue
   

   • Example:

     string name = null;
     string displayName = name ?? "Guest";
     Console.WriteLine(displayName); // Outputs "Guest"
     

2. ternary Operator (?:)

   • A shorthand for simple if-else constructs.

   condition ? true-part : false-part
   

   • Example:

     int value = 20;
     string result = (value > 10) ? "Greater than 10" : "Less than or equal to 10";
     Console.WriteLine(result); // Outputs "Greater than 10"
     

3. ?. Operator (Null Conditional Operator)

   • Checks for null before executing a member access.

   objectVariable?.Member
   

   • Example:

     Person person = null;
     string name = person?.Name; // name will be null if person is null
     Console.WriteLine(name ?? "No Name"); // Outputs "No Name"
     

Control Flow Best Practices

• Readability: Choose the most readable construct for your logic, such as using switch instead of multiple if-else statements when applicable.
• Simplicity: Avoid complicated nested control structures as they can lead to errors and make debugging difficult.
• Exception Handling: Implement appropriate exception handling to gracefully manage errors and ensure program robustness.
• Early Returns: Use early returns to reduce complexity, especially in larger methods.
• Consistent Coding Style: Follow coding standards consistently to ensure that everyone on the team can easily understand the code.

By mastering these control flow statements, developers can create more dynamic and responsive applications in C#. Each statement plays a unique role in controlling the flow of execution and handling data efficiently, which is crucial for building successful software systems.

Important Info Summary

• Conditionals: if, if-else, if-else-if, switch.
• Loops: for, foreach, while, do-while.
• Jumps: break, continue, goto, return.
• Exception Handling: try-catch, throw.
• Null Handling: ?? (null-coalescing), ?: (ternary), ?. (null conditional).

These control structures form the backbone of logic implementation in C#. Proper use leads to better performance, clearer code, and fewer bugs.

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