Part 4: Control Flow in C#

Control flow in a program determines the order in which instructions are executed. In C#, these decisions and repetitions are managed with specific structures that allow you to create dynamic and flexible programs. In this lesson, we will explore the main control flow structures: decisions and loops.

1. Decision Structures

Decision structures allow the program to execute different blocks of code depending on a condition. The most common ones in C# are if, else if, and else.

1.1 if

The if block evaluates a condition and executes the code inside the block if the condition is true.

int number = 10;
if (number > 5)
{
    Console.WriteLine("The number is greater than 5.");
}

1.2 else if

This is used to evaluate additional conditions if the initial condition is not met.

int number = 5;
if (number > 10)
{
    Console.WriteLine("The number is greater than 10.");
}
else if (number == 5)
{
    Console.WriteLine("The number is equal to 5.");
}

1.3 else

The else block is executed if none of the previous conditions are met.

int number = 3;
if (number > 10)
{
    Console.WriteLine("The number is greater than 10.");
}
else if (number == 5)
{
    Console.WriteLine("The number is equal to 5.");
}
else
{
    Console.WriteLine("The number is not greater than 10 nor equal to 5.");
}

2. Loop Structures

Loops or repetition structures allow you to execute a block of code multiple times, making repetitive tasks easier.

2.1 for

The for loop is ideal when you know the exact number of iterations.

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

2.2 while

The while loop executes the code as long as the condition is true.

int counter = 0;
while (counter < 5)
{
    Console.WriteLine($"Counter: {counter}");
    counter++;
}

2.3 do-while

Similar to while, but it ensures that the block of code is executed at least once.

int counter = 0;
do
{
    Console.WriteLine($"Counter: {counter}");
    counter++;
} while (counter < 5);

2.4 foreach

This is used to iterate through collections such as arrays or lists in a simple way.

int[] numbers = {1, 2, 3, 4, 5};
foreach (int number in numbers)
{
    Console.WriteLine(number);
}

3. Practical Exercises

3.1 Calculate the Factorial of a Number

The factorial of a positive integer n is the product of all positive integers less than or equal to n.

int number = 5;
int factorial = 1;
for (int i = 1; i <= number; i++)
{
    factorial *= i;
}
Console.WriteLine($"The factorial of {number} is {factorial}.");

3.2 Consecutive Sums

Calculate the sum of the first n natural numbers.

int n = 10;
int sum = 0;
for (int i = 1; i <= n; i++)
{
    sum += i;
}
Console.WriteLine($"The sum of the first {n} numbers is {sum}.");

3.3 Check if a Number is Prime

A prime number is one that is only divisible by 1 and itself.

int number = 7;
bool isPrime = true;
for (int i = 2; i < number; i++)
{
    if (number % i == 0)
    {
        isPrime = false;
        break;
    }
}
if (isPrime)
{
    Console.WriteLine($"{number} is a prime number.");
}
else
{
    Console.WriteLine($"{number} is not a prime number.");
}