C# by Example: Loops


bool conditional = true;

A while loop has the same structure as an if statement, but it will repeatedly run the code in block until the condition stops being true. Also like an if statement, if it's false (as this one is), it will skip it and never run.


while (conditional)
{
    Console.Write("Run Forever");

The break keyword will end the loop, regardless of the conditional. Without it, this while(true) loop would be an infinite loop, and the program would crash.


    break;
}

The following loop will run 10 times. The counter starts at 0 and goes up till 9. On the last run, it's increased to 10. 10 is not less than 10, so it stops running and the code moves on. That's 10 total runs. The output of this code would be "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
This runs once before the loop


int counter = 0;

The conditional is checked every time, and returns true or false.


while (counter < 10)
{
    Console.Write(counter+", ");

This runs every single time, after the rest of the code above.


    counter++;
}

The syntax of a counter is convenient, so there's a different type of loop that does all these parts too. It's called a for loop. The for loop has the same 3 parts that were written in the previous while loop: a part that runs once at the beginning, a conditional that is checked every time, and a part that runs at the end of each loop. Defined in that order.


for (int i = 0; i < 10; i++)
{
    Console.Write(i+", ");
}

Using a for loop instead of a while loop keeps it so that all of the 'loop control' logic is written in one place, while the 'things we do in a loop' is written elsewhere.


for (int j = 10; j>=0;j--)
{
    Console.WriteLine(j);
}
Console.WriteLine("Blast Off!");

It's a very common pattern to use a for loop to run through all the items in an array once.


string[] someArray = new string[5];


for (int i = 0; i < someArray.Length; i++)
{
    string item = someArray[i];
    if (item == "")
    {

The 'continue' keyword, inside of a loop, will skip ahead to the next iteration.


        continue;
    }else if (item == "should-break")
    {

the 'break' keyword will stop the loop executing entirely.


        break;
    }
}

Further:

Foreach Loops

Next example: Foreach.