# Control Structures and Functions

# 📚 Watch and Read

# Control Structures

To solve real-world problems, we use control structures which allow our code to flow logicly similar to the way our brains do. For example, how would you explain the rules of the game "Rock, Paper, Scissors" to a friend who has never heard it? You might say something like:

1. each player makes a fist
2. each player shakes their fist three times saying 'Rock, Paper, Scissors'
3. each player shakes their fist a fourth time and changes their fist to one of the shapes for rock, paper, or scissors
4. player 1 wins if she chooses rock and player 2 chooses scissors or she chooses paper and player 2 chooses rock or she chooses scissors and player 2 chooses paper

In programming, we use control structures to accomplish logic like this.

After watching the videos above, you may see some places where we could use control structures to write rock, paper, scissors in code.

The rules around who wins could be expressed with if, and, or statements. The && represents AND, the || represents OR.

if (player1 == 'rock' && player2 == 'scissors' ||
    player1 == 'paper' && player2 == 'rock' ||
    player1 == 'scissors' && player2 == 'paper') {
        winner = player1
}

# Procedures, Functions, and Libraries

Functions, also called procedures or methods (there are differences between the three, but for our introductory purposes, they serve the same purpose) allow you to right code once and call it again and again without writing it multiple times. In the example above, we could use a function to play many games of Rock, Paper, Scissors.

function game(player1, player2){
    if (player1 == 'rock' && player2 == 'scissors' ||
        player1 == 'paper' && player2 == 'rock' ||
        player1 == 'scissors' && player2 == 'paper') {

        console.log("winner is " + player1);

    }
}

game("Rock", "Scissors");
game("Paper", "Rock");

We wrote a function called game and used a pre-made function called console.log which the creators of the JavaScript language wrote because they knew that would be a common thing people would need to do and people shouldn't have to write their own code every time they want want to do something as simple as "print something on the screen".

Libraries take this one step further and are groups of related functions. saml2-js is a javascript library for integrating single-sign on to javascript applications. Single-Sign On (SSO) is an often required security practice for enterprise applications and implementing it is complex and requires many functions. When you logon to myRCC and get access to Blackboard, SIS, and other applications with 1 login, that is SSO. The saml2-js library, would allow a developer to integrate their app securely with SSO and is one example of a library that someone has written that includes all the necessary functions to implement SSO in one package.

# Scope

Read What is scope? and watch this lecture on functions and scope which has lots of live coding examples and some audience Q&A.

# Practice on freecodecamp

This video shows a couple ways to watch videos and code in Glitch at the same time.

Complete the lessons below in freeCodeCamp JavaScript course.

1. Write Reusable JavaScript with Functions 💻 code📺 watch
2. Passing Values to Functions with Arguments 💻 code📺 watch
3. Global Scope and Functions 💻 code📺 watch
4. Local Scope and Functions 💻 code📺 watch
5. Global vs. Local Scope in Functions 💻 code📺 watch
6. Return a Value from a Function with Return 💻 code📺 watch
7. Understanding Undefined Value returned from a Function 💻 code📺 watch
8. Assignment with a Returned Value 💻 code📺 watch
9. Stand in Line 💻 code📺 watch
10. Understanding Boolean Values 💻 code📺 watch
11. Use Conditional Logic with If Statements 💻 code📺 watch
12. Comparison with the Equality Operator 💻 code📺 watch
13. Comparison with the Strict Equality Operator 💻 code📺 watch
14. Practice comparing different values 💻 code📺 watch
15. Comparison with the Inequality Operator 💻 code📺 watch
16. Comparison with the Strict Inequality Operator 💻 code📺 watch
17. Comparison with the Greater Than Operator 💻 code📺 watch
18. Comparison with the Greater Than Or Equal To Operator 💻 code📺 watch
19. Comparison with the Less Than Operator 💻 code📺 watch
20. Comparison with the Less Than Or Equal To Operator 💻 code📺 watch
21. Comparisons with the Logical And Operator 💻 code📺 watch
22. Comparisons with the Logical Or Operator 💻 code📺 watch
23. Introducing Else Statements 💻 code📺 watch
24. Introducing Else If Statements 💻 code📺 watch
25. Logical Order in If Else Statements 💻 code📺 watch
26. Chaining If Else Statements 💻 code📺 watch
27. Golf Code 💻 code📺 watch
28. Selecting from Many Options with Switch Statements 💻 code📺 watch
29. Adding a Default Option in Switch Statements 💻 code📺 watch
30. Multiple Identical Options in Switch Statements 💻 code📺 watch
31. Replacing If Else Chains with Switch 💻 code📺 watch
32. Returning Boolean Values from Functions 💻 code📺 watch
33. Return Early Pattern for Functions 💻 code📺 watch
34. Counting Cards 💻 code📺 watch