Control Flow
Lesson 2.3: Control Flow
Control flow determines the order in which statements are executed in your C# program. Without control flow, your code would run from top to bottom, executing each line only once. This lesson explores two essential control flow concepts:
1. Conditional Statements (Decision Making)
Conditional statements allow your program to choose different paths of execution based on certain conditions. The most common type is the if/else statement.
if Statement: Executes a block of code only if a specified condition is true.
C#
int age = 20;
if (age >= 18)
{
Console.WriteLine("You are an adult.");
}
else Statement: Executes a block of code if the if condition is false.
C#
int score = 75;
if (score >= 60)
{
Console.WriteLine("You passed!");
}
else
{
Console.WriteLine("You need to study more.");
}
else if Statement: Allows you to check multiple conditions in sequence.
C#
int grade = 85;
if (grade >= 90)
{
Console.WriteLine("Excellent!");
}
else if (grade >= 80)
{
Console.WriteLine("Great job!");
}
else
{
Console.WriteLine("Keep trying!");
}
2. Loops (Repetition)
Loops let you repeat a block of code multiple times. C# offers three main loop types:
for Loop: Repeats a block of code a specific number of times.
C#
for (int i = 0; i < 5; i++) // Start at 0, continue as long as i is less than 5, increment i by 1 each time
{
Console.WriteLine("Hello!"); // Prints "Hello!" five times
}
Use code with caution.
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while Loop: Repeats a block of code as long as a condition is true.
C#
int count = 0;
while (count < 10)
{
Console.WriteLine(count);
count++;
}
do-while Loop: Similar to a while loop, but the block of code is executed at least once before the condition is checked.
C#
int number = 0;
do
{
Console.WriteLine(number);
number++;
} while (number < 5);
Choosing the Right Loop
Use a for loop when you know exactly how many times you want the loop to run.
Use a while loop when you want to repeat as long as a condition is true, but you don't know the exact number of repetitions in advance.
Use a do-while loop when you need the code inside the loop to execute at least once, even if the condition is initially false.
Example: Putting It Together
C#
Console.WriteLine("Enter your age:");
int age = int.Parse(Console.ReadLine()); // Read age from the user
if (age < 13)
{
Console.WriteLine("You are a child.");
}
else if (age < 18)
{
Console.WriteLine("You are a teenager.");
}
else
{
Console.WriteLine("You are an adult.");
// Count down from the current age to 0
for (int i = age; i >= 0; i--)
{
Console.WriteLine(i);
}
}
Key Takeaways
Control flow makes your programs dynamic and responsive.
Conditional statements allow your code to make decisions.
Loops automate repetitive tasks, making your programs more efficient.