theme: Next, 1

[fit] Control Flow

Control Flow

Sequential lines of code are evaluated in a row.

To make decisions and take different paths we need control flow

If Statements

Simplest of the control flow statements.

Basic structure:

if (someBooleanCondition) {
  // Code to run if the condition is true
}

If / Else statements

Can also handle the case when the condition is false

if (someBooleanCondition) {
  // Code if the condition is true
}
else {
  // Code if the condition is false
}

^ The part someBooleanCondition can be a boolean variable or a condition that evaluates to a boolean value.

Boolean Conditions

Examples of boolean conditions

Example

if (name == "Paul") {
  Console.WriteLine("Greetings!");
} else {
  Console.WriteLine("Wait, who are you?");
}

Multiple Booleans: Or, And

Combine two conditions.

Or is written as || while And is written as &&

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Condition that is true if the score is lower than 20 OR greater than 90:

if (score < 20 || score > 90) {
  // Some code here
}

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Condition that is true if the person is named Paul AND the score is more than 85:

if (name == "Paul" && score > 85) {
  // Some code here
}

Truth Table

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A && B

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A || B

^ Don't memorize these, but if you can remember them it will help you write better if statements

Chaining

A series of if/else statements can be chained.

if (name == "Paul") {
  Console.WriteLine("Here");
} else if (name == "Dorothy") {
  Console.WriteLine("Also here");
} else if (name == "Sam") {
  Console.WriteLine("Here again");
} else {
  Console.WriteLine("Didn't find anything");
}

[fit] We can do better

Introducing switch

switch (name)
{
    case "Paul":
        Console.WriteLine("Here");
        break;
    case "Dorothy":
        Console.WriteLine("Also Here");
        break;
    case "Sam":
        Console.WriteLine("Here Again");
        break;
    default:
        Console.WriteLine("Didn't find anything");
        break;
}

Other neat switch features

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We can handle multiple values by repeating the case statement:

In this code we will see the message Here for name if it is either Paul OR Peter OR Mary

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switch (name)
{
    case "Paul":
    case "Peter":
    case "Mary":
        Console.WriteLine("Here");
        break;
    case "Dorothy":
        Console.WriteLine("Also Here");
        break;
    case "Sam":
        Console.WriteLine("Here Again");
        break;
    default:
        Console.WriteLine("Didn't find anything");
        break;
}

Case conditionals

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Let's say we are working with an int variable named score and we wanted to print a grade associated to a score.

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var score = 95;
switch (score)
{
    case < 65:
        Console.WriteLine("F");
        break;
    case < 70:
        Console.WriteLine("D");
        break;
    case < 80:
        Console.WriteLine("C");
        break;
    case < 90:
        Console.WriteLine("B");
        break;
    case >= 90:
        Console.WriteLine("A");
        break;
    default:
        Console.WriteLine("Hmmm, I don't recognize this score");
        break;
}

[fit] What about repeating code?

What about repeating code?

What about repeating code?

What about repeating code?

🐢🐢🐢🐢🐢🐢🐢🐢

[fit] Loops

[fit] while

While

The while statement repeats the code inside the { } braces as long as the condition supplied remains true.

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Ask the user their name and greet them until the user enters the text quit. The code would look like this:

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Console.Write("What is your name? ");
var name = Console.ReadLine();
while (name != "quit") {
  Console.WriteLine($"Hello {name}");
  Console.Write("What is your name? ");
  name = Console.ReadLine();
}