C# Lesson 5 - Loops

One other thing computers are very good at is repeating instruction aka. Loops or Iteration.

There are 3 main kind of loops

• For Loops
• Do Loops
• While Loops

While Loop

The following program repeats while ‘i’ is greater than zero

Note the use of i--, this takes one off whatever the value of ‘i’ is. It is a shorter version of writing i=i-1

static void Main(string[] args) { int i = 10; while (i>0) { i--;//Subtract 1 from i Console.WriteLine("i=" + i); } //press a key to exit Console.ReadKey(); }

While Loops are used in all the programs you currently have running!

While(true)

{

    //Run program

}

Only when you exit the program does this loop end, use carefully!

Do Loop

static void Main(string[] args) { int i = 10; do { i--; Console.WriteLine("i=" + i); } while (i > 0); //press a key to exit Console.ReadKey(); }

Both the while and the do loop appear to do the exact same thing. The difference is a While loop may never run, where as a Do Loop will always run at least once.

Activity

Changing the i=10 line to i=0 in both loops and see the difference!

For Loops

For Loops will be the loop you are likely to use the most.  

static void Main(string[] args) { for (int i=0;i<10;i++) { Console.WriteLine("i=" + i); } //press a key to exit Console.ReadKey(); }

Activity

Write a program that will;

Output the square of each number up to and including 20

Output the Square Root of the numbers between 2 and 25

Make you output for program 1 look like this