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.");
}
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