Looping

Often in programming, we need to perform a task repeatedly or we need to process all of the items in some collection. For these situations we can use the idea of loops.

Let's say we want to perform some statement, or statements, 10 times. We could do this with the while control flow statement as follows:

var counter = 0;
while (counter < 10) {
  Console.WriteLine("Doing something");
  counter++;
}

NOTE that counter++ is a shortcut for counter = counter + 1

This kind of loop is so common that we have a special syntax for it, the for loop. The basic structure of a for loop is:

for(INITIALIZATION; CONDITION; AFTERTHOUGHT) {
  // Loop statements
}

The code that goes in the INITIALIZATION often initializes a variable that will be used in the CONDITION and the AFTERTHOUGHT.

for (var counter = 0; counter < 10; counter++) {
  Console.WriteLine("Doing something");
}

As you can see, all the elements of the while loop have their own place in the for loop example.

Another way to read the for loop is Start the counter at 0 and as long as the value of counter is less than 10, do the contents of the loop and then increment counter.

Looping through an array

The for loop is also helpful for processing all the elements of an array or List.

string[] names = { "Mark", "Paula", "Sandy" , "Bill" };

If we wanted to print all the individual names in the array we could write a loop like:

for (var index = 0; index < names.Length; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}

In this case we start the index at 0 since our array index starts at 0. And we want to keep the loop going as long as the index stays less than the length of the array (again, since array indexes start at 0 and end one index before the value of their length).

This code works well but there is an even more succinct syntax called foreach.

foreach (var name in names) {
  Console.WriteLine(name);
}

The foreach method assumes we are going to work through the entire array.

Looping through List

Fortunately the for loop and foreach loop work similarly for a List

var names = new List<string>() { "Mark", "Paula", "Sandy" , "Bill" };
foreach (var name in names) {
  Console.WriteLine(name);
}

var names = new List<string>() { "Mark", "Paula", "Sandy" , "Bill" };
for (var index = 0; index < names.Count; index++) {
  var name = names[index];
  Console.WriteLine(name);
}