Loops in C# are used to execute a block of code repeatedly until a specified condition is met. They are essential for tasks that require repetitive actions. This tutorial covers various types of loops in C#, including `for`, `foreach`, `while`, `do-while` loops, and `List.ForEach`.
| Loop Type | Description |
|---|---|
| for | Executes a block of code a specified number of times, based on a counter variable. |
| foreach | Iterates through each element in a collection or array. |
| while | Executes a block of code as long as a specified condition is true. |
| do-while | Executes a block of code at least once, and then repeatedly executes the block as long as a specified condition is true. |
| List.ForEach | Executes a specified action on each element of a list. |
The for loop executes a block of code a specified number of times, based on a counter variable.
Basic Example:
namespace LoopExamples;
class Program
{
static void Main(string[] args)
{
for (int i = 0; i < 5; i++)
{
Console.WriteLine($"Iteration: {i}");
}
}
}
namespace LoopExamples;
class Program
{
static void Main(string[] args)
{
for (int i = 0, j = 10; i < j; i++, j--)
{
Console.WriteLine($"i: {i}, j: {j}");
}
int[] numbers = { 1, 2, 3, 4, 5 };
for (int i = 0; i < numbers.Length; i++)
{
Console.WriteLine($"Number: {numbers[i]}");
}
}
}
The foreach loop iterates through each element in a collection or array.
Basic Example:
namespace LoopExamples;
class Program
{
static void Main(string[] args)
{
string[] names = { "Alice", "Bob", "Charlie" };
foreach (var name in names)
{
Console.WriteLine($"Name: {name}");
}
}
}
namespace LoopExamples;
class Program
{
static void Main(string[] args)
{
var people = new List<Person>
{
new Person { Name = "Alice", Age = 30 },
new Person { Name = "Bob", Age = 25 },
new Person { Name = "Charlie", Age = 35 }
};
foreach (var person in people)
{
Console.WriteLine($"Name: {person.Name}, Age: {person.Age}");
}
}
}
class Person
{
public string Name { get; set; }
public int Age { get; set; }
}
The while loop executes a block of code as long as a specified condition is true.
Basic Example:
namespace LoopExamples;
class Program
{
static void Main(string[] args)
{
int counter = 0;
while (counter < 5)
{
Console.WriteLine($"Counter: {counter}");
counter++;
}
}
}
namespace LoopExamples;
class Program
{
static void Main(string[] args)
{
int number = 10;
while (number >= 0)
{
Console.WriteLine($"Number: {number}");
number -= 2;
}
// Infinite loop with a break condition
int sum = 0;
while (true)
{
sum += 1;
if (sum > 10)
break;
}
Console.WriteLine($"Sum: {sum}");
}
}
The do-while loop executes a block of code at least once, and then repeatedly executes the block as long as a specified condition is true.
Basic Example:
namespace LoopExamples;
class Program
{
static void Main(string[] args)
{
int counter = 0;
do
{
Console.WriteLine($"Counter: {counter}");
counter++;
} while (counter < 5);
}
}
namespace LoopExamples;
class Program
{
static void Main(string[] args)
{
int number;
do
{
Console.WriteLine("Enter a number greater than 0:");
number = int.Parse(Console.ReadLine());
} while (number <= 0);
Console.WriteLine($"You entered: {number}");
}
}
The List.ForEach method executes a specified action on each element of a list. This method is convenient and can be used for simple operations on each list element.
Basic Example:
namespace LoopExamples;
class Program
{
static void Main(string[] args)
{
List<int> numbers = new() { 1, 2, 3, 4, 5 };
numbers.ForEach(number => Console.WriteLine(number));
}
}
namespace LoopExamples;
class Program
{
static void Main(string[] args)
{
List<Person> people = new()
{
new Person { Name = "Alice", Age = 30 },
new Person { Name = "Bob", Age = 25 },
new Person { Name = "Charlie", Age = 35 }
};
people.ForEach(person =>
{
Console.WriteLine($"Name: {person.Name}, Age: {person.Age}");
person.Age += 1; // Modifying the elements within the loop
});
Console.WriteLine("After modification:");
people.ForEach(person => Console.WriteLine($"Name: {person.Name}, Age: {person.Age}"));
}
}
class Person
{
public string Name { get; set; }
public int Age { get; set; }
}
for Loop: Use when you need to iterate a specific number of times or when you need access to the index of the current iteration.
foreach Loop: Use when you need to iterate over all elements in a collection or array and do not need access to the index of the current element.
while Loop: Use when the number of iterations is not known before entering the loop and the loop should continue as long as a condition is true.
do-while Loop: Use when you need to ensure the loop executes at least once, regardless of the condition.
List.ForEach: Use when you need to perform simple operations on each element of a list. It is a concise and readable way to apply an action to each element.
Understanding and using loops effectively is crucial for handling repetitive tasks in C#. This tutorial covered various types of loops, including for, foreach, while, do-while loops, and List.ForEach, along with best practices for using them.