theme: Next,1

[fit] Looping

• Perform a task repeatedly or a certain number of times

• Perform a task repeatedly until a condition is met

• Process all of the items in a collection

We've seen this with the while control flow:

Do something 10 times.

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

^ counter++ is a shortcut for counter = counter + 1

Introducing for loop

// Do this at the start
//      |
//      |        Keep going as long as this is true
//      |               |
//      |               |     Do this after each loop is done
//      |               |         |
//      |               |         |
//      V               V         V
for(INITIALIZATION; CONDITION; AFTERTHOUGHT) {
  // Loop statements
}

[fit] Revisiting printing something 10 times

// Start the counter at 0
//      |
//      |        Keep going as long as counter is less than 10
//      |               |
//      |               |        Increment counter after each loop is done
//      |               |             |
//      |               |             |
//      V               V             V
for (var counter = 0; counter < 10; counter++) {
  Console.WriteLine("Doing something");
}

^ 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 a List

var names = new List<string>() { "Mark", "Paula", "Sandy" };

Let's loop through this list and print out each name.

// Start the index at 0
//      |
//      |        Keep going as long as index is less than the length of the list
//      |                 |
//      |                 |        Increment index after each loop is done
//      |                 |                   |
//      |                 |                   |
//      v                 v                   v
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

Pretending we are .NET

It is often helpful to imagine we are .NET and walk through the code and see it how the computer does

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

[.code-highlight:1]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

Make a List of three strings.

names    =>  "Mark", "Paula", "Sandy"

[.column]

[.code-highlight:3]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

First time at this loop. Do the initialization. Make index equal to 0

[.code-highlight:2]

names   =>  "Mark", "Paula", "Sandy"
index   =>  0

[.column]

[.code-highlight:4]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

Make currentName equal to whatever is at the index given by index. Well index is 0 so that makes currentName equal to "Mark"

[.code-highlight:3]

names       =>  "Mark", "Paula", "Sandy"
index       =>  0
currentName =>  "Mark"

[.column]

[.code-highlight:6]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

Call the method Console.WriteLine and provide it the value in currentName which is currently "Mark"

[.code-highlight:3]

names       =>  "Mark", "Paula", "Sandy"
index       =>  0
currentName =>  "Mark"

[.column]

[.code-highlight:7]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

End of the loop, so do the afterthought step of index++, turning the value of 0 to 1

[.code-highlight:2]

names       =>  "Mark", "Paula", "Sandy"
index       =>  1
currentName =>  "Mark"

[.column]

[.code-highlight:3]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

Back to the loop. Since currentName is defined inside the loop we forget that variable. Time to do the comparison. Is index (1) less than names.Count (3). Yes, so do the loop again.

[.code-highlight:2]

names       =>  "Mark", "Paula", "Sandy"
index       =>  1

[.column]

[.code-highlight:4]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

Make currentName equal to whatever is at the index given by index. Well index is 1 so that makes currentName equal to "Paula"

[.code-highlight:3]

names         =>  "Mark", "Paula", "Sandy"
index         =>  1
currentName   =>  "Paula"

[.column]

[.code-highlight:6]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

Call the method Console.WriteLine and provide it the value in currentName which is currently "Paula"

[.code-highlight:3]

names       =>  "Mark", "Paula", "Sandy"
index       =>  1
currentName =>  "Paula"

[.column]

[.code-highlight:7]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

End of the loop, so do the afterthought step of index++, turning the value of 1 to 2

[.code-highlight:2]

names       =>  "Mark", "Paula", "Sandy"
index       =>  2
currentName =>  "Paula"

[.column]

[.code-highlight:3]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

Back to the loop. Since currentName is defined inside the loop we forget that variable. Time to do the comparison. Is index (2) less than names.Count (3). Yes, so do the loop again.

[.code-highlight:2]

names       =>  "Mark", "Paula", "Sandy"
index       =>  2

[.column]

[.code-highlight:4]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

Make currentName equal to whatever is at the index given by index. Well index is 2 so that makes currentName equal to "Sandy"

[.code-highlight:3]

names         =>  "Mark", "Paula", "Sandy"
index         =>  2
currentName   =>  "Sandy"

[.column]

[.code-highlight:6]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

Call the method Console.WriteLine and provide it the value in currentName which is currently "Sandy"

[.code-highlight:3]

names       =>  "Mark", "Paula", "Sandy"
index       =>  2
currentName =>  "Sandy"

[.column]

[.code-highlight:7]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

End of the loop, so do the afterthought step of index++, turning the value of 2 to 3

[.code-highlight:2]

names       =>  "Mark", "Paula", "Sandy"
index       =>  3
currentName =>  "Paula"

[.column]

[.code-highlight:3]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

Back to the loop. Since currentName is defined inside the loop we forget that variable. Time to do the comparison. Is index (3) less than names.Count (3). No! So we leave the loop, moving to the code AFTER the loop

[.code-highlight:2]

names       =>  "Mark", "Paula", "Sandy"
index       =>  3

[.column]

[.code-highlight:9]

var names = new List<string>() { "Mark", "Paula", "Sandy" };
for (var index = 0; index < names.Count; index++) {
  var currentName = names[index];
  Console.WriteLine(currentName);
}
Console.WriteLine("Hi, this is code after the loop");

[.column]

We are now out of the loop, and since index was defined inside the loop we forget about that variable as well.

names       =>  "Mark", "Paula", "Sandy"

[fit] Whew!

shorter syntax

foreach

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

^ Assumes you are going to loop through the entire list.