Loops in C# for loops while and do while loop.

C#
LECTURE#7
Abid Kohistani
GC Madyan Swat

Loops
Loops can execute a block of code as long as a specified condition is reached.
Loops are handy because they save time, reduce errors, and they make code more readable.
 Programming languages provide various control structures that allow for
more complicated execution paths.
 A loop statement allows us to execute a statement or group of statements
multiple times and following is the general from of a loop statement in
most of the programming languages:

While Loop
The while loop loops through a block of code as long as a specified condition is True:
In the example below, the code in the loop will run, over and over again, as long as a variable (i) is less than 5:
while (condition)
{
// code block to be executed
}
int i = 0;
while (i < 5)
{
Console.WriteLine(i);
i++;
}

The Do/While Loop
The do/while loop is a variant of the while loop. This loop will execute the code block once, before
checking if the condition is true, then it will repeat the loop as long as the condition is true.
Syntax:
Example:
do
{
} while (condition);
int i = 0;
do
{
i++;
} while (i < 5);

For Loop
When you know exactly how many times you want to loop through a block of code, use the for loop instead
of a while loop:
for (statement 1; statement 2; statement 3)
{
}
Syntax
for (int i = 0; i < 5; i++)
{
}
Example
Statement 1 is executed (one time) before the execution
of the code block.
Statement 2 defines the condition for executing the code
block.
Statement 3 is executed (every time) after the code
block has been executed.

The foreach Loop
There is also a foreach loop, which is used exclusively to loop through elements in an array:
The example outputs all elements in the cars array, using a foreach loop:
foreach (type variableName in arrayName)
{
}
Syntax
string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
foreach (string i in cars)
{
}
Example

Arrays
Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each
value. To declare an array, define the variable type with square brackets:
We have now declared a variable that holds an array of strings. To insert values to it, we can use an array
literal - place the values in a comma-separated list, inside curly braces:
To create an array of integers, you could write:
string[] cars;
int[] myNum = {10, 20, 30, 40};

Access the Elements of an Array
You access an array element by referring to the index number. This statement accesses the value of the first
element in cars:
To change the value of a specific element, refer to the index number:
To find out how many elements an array has, use the Length property:
Console.WriteLine(cars[0]); // Outputs Volvo
cars[0] = "Opel";
Console.WriteLine(cars[0]); // Now outputs Opel instead of Volvo
Example
Console.WriteLine(cars.Length); // Outputs 4
Example

Loop Through an Array
You can loop through the array elements with the for loop, and use the Length property to specify how
many times the loop should run. The following example outputs all elements in the cars array:
for (int i = 0; i < cars.Length; i++)
{
Console.WriteLine(cars[i]);
}
Example

The foreach Loop
There is also a foreach loop, which is used exclusively to loop through elements in an array:
The example below can be read like this: for each string element (called i - as in index) in cars, print out the
value of i. If you compare the for loop and foreach loop, you will see that the foreach method is easier to
write, it does not require a counter (using the Length property), and it is more readable.
{
}
Example

Sort Arrays
There are many array methods available, for example Sort(), which sorts an array alphabetically or in an
ascending order:
// Sort a string
Array.Sort(cars);
{
}
Example 1
// Sort an int
int[] myNumbers = {5, 1, 8, 9};
Array.Sort(myNumbers);
foreach (int i in myNumbers)
{
}
Example 2

System.Linq Namespace
Other useful array methods, such as Min, Max, and Sum, can be found in the System.Linq namespace:
using System;
using System.Linq;
namespace MyApplication
{
class Program
{
static void Main(string[] args)
{
int[] myNumbers = {5, 1, 8, 9};
Console.WriteLine(myNumbers.Max()); // returns the largest value
Console.WriteLine(myNumbers.Min()); // returns the smallest value
Console.WriteLine(myNumbers.Sum()); // returns the sum of elements
}
}
}
Example 1

Other Ways to Create an Array
// Create an array of four elements, and add values later
string[] cars = new string[4];
// Create an array of four elements and add values right away
string[] cars = new string[4] {"Volvo", "BMW", "Ford", "Mazda"};
// Create an array of four elements without specifying the size
string[] cars = new string[] {"Volvo", "BMW", "Ford", "Mazda"};
// Create an array of four elements, omitting the new keyword, and without specifying the size

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